Q1. Which of the following is NOT an indication that a chemical reaction has taken place?

Difficulty: Easy · Topic: Chemical Reactions

Solution

A chemical reaction is indicated by changes such as colour change, gas evolution, temperature change, or precipitate formation. A change in the shape of the container is a physical change, not a chemical one.

Q2. The green coating formed on copper vessels left in air is due to the formation of:

Difficulty: Easy · Topic: Corrosion and Rancidity

Solution

Copper reacts with moist carbon dioxide in the air to form a green coating of basic copper carbonate: Cu(OH)₂·CuCO₃. This is why copper vessels and statues (like the Statue of Liberty) turn green over time.

Q3. A balanced chemical equation has equal number of:

Difficulty: Easy · Topic: Chemical Reactions

Solution

According to the Law of Conservation of Mass, matter can neither be created nor destroyed. Therefore, a balanced chemical equation must have the same number of atoms of each element on the reactant side and the product side.

Q4. How many atoms of O are present in 12 molecules of H2O?

A) 14
B) 13
C) 12
D) 1

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

12 molecules contain 12 x 1 = 12 atoms of O.

Q5. How many atoms of O are present in 20 molecules of Ca(OH)2?

A) 2
B) 20
C) 40
D) 22

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

20 molecules contain 20 x 2 = 40 atoms of O.

Q6. How many atoms of H are present in 4 molecules of H2SO4?

A) 6
B) 4
C) 2
D) 8

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 2 atom(s) of H.

4 molecules contain 4 x 2 = 8 atoms of H.

Q7. How many atoms of O are present in 20 molecules of H2O?

A) 1
B) 21
C) 20
D) 22

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

20 molecules contain 20 x 1 = 20 atoms of O.

Q8. How many atoms of Cl are present in 12 molecules of CaCl2?

A) 12
B) 14
C) 2
D) 24

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CaCl2 has 2 atom(s) of Cl.

12 molecules contain 12 x 2 = 24 atoms of Cl.

Q9. How many atoms of H are present in 19 molecules of C6H12O6?

A) 31
B) 19
C) 12
D) 228

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

19 molecules contain 19 x 12 = 228 atoms of H.

Q10. How many atoms of H are present in 19 molecules of NH3?

A) 19
B) 57
C) 3
D) 22

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

19 molecules contain 19 x 3 = 57 atoms of H.

Q11. How many atoms of O are present in 18 molecules of Al2O3?

A) 54
B) 18
C) 21
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Al2O3 has 3 atom(s) of O.

18 molecules contain 18 x 3 = 54 atoms of O.

Q12. How many atoms of H are present in 15 molecules of C6H12O6?

A) 15
B) 180
C) 27
D) 12

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

15 molecules contain 15 x 12 = 180 atoms of H.

Q13. How many atoms of Cl are present in 19 molecules of CaCl2?

A) 2
B) 19
C) 38
D) 21

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CaCl2 has 2 atom(s) of Cl.

19 molecules contain 19 x 2 = 38 atoms of Cl.

Q14. How many atoms of O are present in 6 molecules of H2O?

A) 7
B) 8
C) 6
D) 1

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

6 molecules contain 6 x 1 = 6 atoms of O.

Q15. How many atoms of O are present in 17 molecules of H2O?

A) 19
B) 17
C) 1
D) 18

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

17 molecules contain 17 x 1 = 17 atoms of O.

Q16. How many atoms of O are present in 16 molecules of Ca(OH)2?

A) 32
B) 2
C) 18
D) 16

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

16 molecules contain 16 x 2 = 32 atoms of O.

Q17. How many atoms of H are present in 9 molecules of H2O?

A) 2
B) 11
C) 18
D) 9

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 2 atom(s) of H.

9 molecules contain 9 x 2 = 18 atoms of H.

Q18. How many atoms of O are present in 5 molecules of CO2?

A) 2
B) 7
C) 5
D) 10

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CO2 has 2 atom(s) of O.

5 molecules contain 5 x 2 = 10 atoms of O.

Q19. How many atoms of O are present in 6 molecules of Ca(OH)2?

A) 12
B) 6
C) 2
D) 8

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

6 molecules contain 6 x 2 = 12 atoms of O.

Q20. How many atoms of H are present in 2 molecules of C6H12O6?

A) 14
B) 2
C) 12
D) 24

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

2 molecules contain 2 x 12 = 24 atoms of H.

Q21. How many atoms of O are present in 15 molecules of H2O?

A) 17
B) 15
C) 16
D) 1

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

15 molecules contain 15 x 1 = 15 atoms of O.

Q22. How many atoms of O are present in 7 molecules of H2SO4?

A) 7
B) 11
C) 28
D) 4

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 4 atom(s) of O.

7 molecules contain 7 x 4 = 28 atoms of O.

Q23. How many atoms of O are present in 2 molecules of Ca(OH)2?

A) 4
B) 6
C) 5
D) 2

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

2 molecules contain 2 x 2 = 4 atoms of O.

Q24. How many atoms of O are present in 10 molecules of H2O?

A) 10
B) 1
C) 11
D) 12

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

10 molecules contain 10 x 1 = 10 atoms of O.

Q25. How many atoms of O are present in 17 molecules of CO2?

A) 34
B) 2
C) 17
D) 19

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CO2 has 2 atom(s) of O.

17 molecules contain 17 x 2 = 34 atoms of O.

Q26. How many atoms of O are present in 10 molecules of Ca(OH)2?

A) 10
B) 2
C) 20
D) 12

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

10 molecules contain 10 x 2 = 20 atoms of O.

Q27. How many atoms of Cl are present in 17 molecules of CaCl2?

A) 34
B) 19
C) 17
D) 2

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CaCl2 has 2 atom(s) of Cl.

17 molecules contain 17 x 2 = 34 atoms of Cl.

Q28. How many atoms of Cl are present in 13 molecules of CaCl2?

A) 26
B) 2
C) 15
D) 13

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CaCl2 has 2 atom(s) of Cl.

13 molecules contain 13 x 2 = 26 atoms of Cl.

Q29. How many atoms of O are present in 7 molecules of Ca(OH)2?

A) 7
B) 2
C) 14
D) 9

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

7 molecules contain 7 x 2 = 14 atoms of O.

Q30. How many atoms of H are present in 7 molecules of C6H12O6?

A) 19
B) 84
C) 7
D) 12

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

7 molecules contain 7 x 12 = 84 atoms of H.

Q31. How many atoms of H are present in 6 molecules of H2O?

A) 6
B) 12
C) 2
D) 8

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 2 atom(s) of H.

6 molecules contain 6 x 2 = 12 atoms of H.

Q32. How many atoms of O are present in 6 molecules of Al2O3?

A) 9
B) 3
C) 6
D) 18

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Al2O3 has 3 atom(s) of O.

6 molecules contain 6 x 3 = 18 atoms of O.

Q33. How many atoms of H are present in 10 molecules of C6H12O6?

A) 120
B) 12
C) 22
D) 10

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

10 molecules contain 10 x 12 = 120 atoms of H.

Q34. Which method is used to prevent corrosion of copper?

A) Lacquering or clear coating
B) Galvanizing
C) Electroplating with iron
D) Adding salt water

Difficulty: Easy · Topic: Prevention of corrosion

Solution

Corrosion of copper is prevented by: Lacquering or clear coating

This works by preventing contact of metal with moisture and oxygen.

Q35. Which method is used to prevent corrosion of iron (galvanizing)?

A) Adding water
B) Galvanizing (coating with zinc)
C) Heating to high temperature
D) Coating with copper

Difficulty: Easy · Topic: Prevention of corrosion

Solution

Corrosion of iron (galvanizing) is prevented by: Galvanizing (coating with zinc)

This works by preventing contact of metal with moisture and oxygen.

Q36. Which method is used to prevent corrosion of iron (electroplating)?

A) Dipping in salt solution
B) Wrapping in wet cloth
C) Heating in water vapour
D) Electroplating with chromium or tin

Difficulty: Easy · Topic: Prevention of corrosion

Solution

Corrosion of iron (electroplating) is prevented by: Electroplating with chromium or tin

This works by preventing contact of metal with moisture and oxygen.

Q37. Which method is used to prevent corrosion of iron (alloying)?

A) Coating with sodium
B) Alloying (e.g., stainless steel with Cr and Ni)
C) Mixing with water
D) Dissolving in acid

Difficulty: Easy · Topic: Prevention of corrosion

Solution

Corrosion of iron (alloying) is prevented by: Alloying (e.g., stainless steel with Cr and Ni)

This works by preventing contact of metal with moisture and oxygen.

Q38. Which method is used to prevent corrosion of iron (painting)?

A) Electroplating with sodium
B) Exposing to moisture
C) Painting or oiling
D) Heating in oxygen

Difficulty: Easy · Topic: Prevention of corrosion

Solution

Corrosion of iron (painting) is prevented by: Painting or oiling

This works by preventing contact of metal with moisture and oxygen.

Q39. Which statement about soap preparation is correct?

A) Soap is a mineral compound
B) Soap is made from petroleum products
C) Soap is made by mixing salt and water
D) Soap is made by saponification of fat/oil with NaOH

Difficulty: Easy · Topic: Soap vs Detergent properties

Solution

Regarding soap preparation:

Soap is made by saponification of fat/oil with NaOH

Q40. Which statement about detergents in hard water is correct?

A) Detergents make water harder
B) Detergents form scum in hard water
C) Detergents cannot clean in hard water
D) Detergents work effectively even in hard water

Difficulty: Easy · Topic: Soap vs Detergent properties

Solution

Regarding detergents in hard water:

Detergents work effectively even in hard water

Q41. Which statement about micelle formation is correct?

A) Micelles have hydrophilic tails inward
B) Micelles are formed only by detergents, not soaps
C) Micelles dissolve in oil completely
D) Soap molecules arrange in micelles with hydrophobic tails inward trapping grease

Difficulty: Easy · Topic: Soap vs Detergent properties

Solution

Regarding micelle formation:

Soap molecules arrange in micelles with hydrophobic tails inward trapping grease

Q42. Which statement about biodegradability is correct?

A) Soaps are not biodegradable
B) Both are equally biodegradable
C) Soaps are biodegradable while some detergents are not
D) Detergents are always biodegradable

Difficulty: Easy · Topic: Soap vs Detergent properties

Solution

Regarding biodegradability:

Soaps are biodegradable while some detergents are not

Q43. Which statement about soaps in hard water is correct?

A) Soaps work better in hard water
B) Soaps form scum (insoluble precipitate) in hard water
C) Soaps dissolve Ca/Mg ions
D) Hard water has no effect on soaps

Difficulty: Easy · Topic: Soap vs Detergent properties

Solution

Regarding soaps in hard water:

Soaps form scum (insoluble precipitate) in hard water

Q44. How many atoms of H are present in 3 molecules of C6H12O6?

A) 15
B) 12
C) 36
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

3 molecules contain 3 x 12 = 36 atoms of H.

Q45. How many atoms of H are present in 9 molecules of H2SO4?

A) 11
B) 2
C) 9
D) 18

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 2 atom(s) of H.

9 molecules contain 9 x 2 = 18 atoms of H.

Q46. How many atoms of H are present in 6 molecules of C6H12O6?

A) 12
B) 18
C) 6
D) 72

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

6 molecules contain 6 x 12 = 72 atoms of H.

Q47. How many atoms of H are present in 16 molecules of H2SO4?

A) 16
B) 32
C) 18
D) 2

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 2 atom(s) of H.

16 molecules contain 16 x 2 = 32 atoms of H.

Q48. How many atoms of O are present in 11 molecules of H2SO4?

A) 11
B) 4
C) 15
D) 44

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 4 atom(s) of O.

11 molecules contain 11 x 4 = 44 atoms of O.

Q49. How many atoms of H are present in 3 molecules of H2SO4?

A) 5
B) 6
C) 2
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 2 atom(s) of H.

3 molecules contain 3 x 2 = 6 atoms of H.

Q50. How many atoms of Cl are present in 4 molecules of CaCl2?

A) 2
B) 8
C) 6
D) 4

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CaCl2 has 2 atom(s) of Cl.

4 molecules contain 4 x 2 = 8 atoms of Cl.

Q51. How many atoms of O are present in 3 molecules of H2O?

A) 4
B) 1
C) 3
D) 5

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

3 molecules contain 3 x 1 = 3 atoms of O.

Q52. How many atoms of O are present in 8 molecules of Ca(OH)2?

A) 2
B) 16
C) 8
D) 10

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

8 molecules contain 8 x 2 = 16 atoms of O.

Q53. How many atoms of O are present in 14 molecules of Al2O3?

A) 14
B) 17
C) 42
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Al2O3 has 3 atom(s) of O.

14 molecules contain 14 x 3 = 42 atoms of O.

Q54. How many atoms of H are present in 2 molecules of H2SO4?

A) 6
B) 2
C) 4
D) 5

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 2 atom(s) of H.

2 molecules contain 2 x 2 = 4 atoms of H.

Q55. How many atoms of H are present in 14 molecules of NH3?

A) 14
B) 42
C) 17
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

14 molecules contain 14 x 3 = 42 atoms of H.

Q56. How many atoms of H are present in 15 molecules of H2O?

A) 17
B) 2
C) 15
D) 30

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 2 atom(s) of H.

15 molecules contain 15 x 2 = 30 atoms of H.

Q57. How many atoms of H are present in 20 molecules of C6H12O6?

A) 32
B) 20
C) 12
D) 240

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

20 molecules contain 20 x 12 = 240 atoms of H.

Q58. How many atoms of H are present in 5 molecules of H2O?

A) 2
B) 5
C) 7
D) 10

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 2 atom(s) of H.

5 molecules contain 5 x 2 = 10 atoms of H.

Q59. How many atoms of H are present in 5 molecules of NH3?

A) 15
B) 8
C) 5
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

5 molecules contain 5 x 3 = 15 atoms of H.

Q60. How many atoms of H are present in 20 molecules of NH3?

A) 60
B) 20
C) 23
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

20 molecules contain 20 x 3 = 60 atoms of H.

Q61. How many atoms of H are present in 16 molecules of NH3?

A) 3
B) 48
C) 16
D) 19

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

16 molecules contain 16 x 3 = 48 atoms of H.

Q62. How many atoms of O are present in 14 molecules of CO2?

A) 14
B) 28
C) 16
D) 2

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CO2 has 2 atom(s) of O.

14 molecules contain 14 x 2 = 28 atoms of O.

Q63. How many atoms of H are present in 7 molecules of NH3?

A) 3
B) 7
C) 21
D) 10

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

7 molecules contain 7 x 3 = 21 atoms of H.

Q64. How many atoms of H are present in 8 molecules of H2SO4?

A) 8
B) 16
C) 2
D) 10

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 2 atom(s) of H.

8 molecules contain 8 x 2 = 16 atoms of H.

Q65. How many atoms of O are present in 2 molecules of H2SO4?

A) 8
B) 6
C) 4
D) 2

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 4 atom(s) of O.

2 molecules contain 2 x 4 = 8 atoms of O.

Q66. How many atoms of H are present in 9 molecules of C6H12O6?

A) 12
B) 9
C) 21
D) 108

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

9 molecules contain 9 x 12 = 108 atoms of H.

Q67. How many atoms of O are present in 9 molecules of H2SO4?

A) 13
B) 9
C) 4
D) 36

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 4 atom(s) of O.

9 molecules contain 9 x 4 = 36 atoms of O.

Q68. How many atoms of O are present in 4 molecules of Ca(OH)2?

A) 8
B) 4
C) 6
D) 2

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

4 molecules contain 4 x 2 = 8 atoms of O.

Q69. How many atoms of H are present in 6 molecules of H2SO4?

A) 2
B) 6
C) 12
D) 8

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 2 atom(s) of H.

6 molecules contain 6 x 2 = 12 atoms of H.

Q70. How many atoms of O are present in 11 molecules of H2O?

A) 12
B) 1
C) 13
D) 11

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

11 molecules contain 11 x 1 = 11 atoms of O.

Q71. How many atoms of O are present in 11 molecules of Al2O3?

A) 3
B) 33
C) 14
D) 11

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Al2O3 has 3 atom(s) of O.

11 molecules contain 11 x 3 = 33 atoms of O.

Q72. How many atoms of O are present in 16 molecules of Al2O3?

A) 48
B) 16
C) 3
D) 19

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Al2O3 has 3 atom(s) of O.

16 molecules contain 16 x 3 = 48 atoms of O.

Q73. How many atoms of O are present in 13 molecules of CO2?

A) 2
B) 26
C) 15
D) 13

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CO2 has 2 atom(s) of O.

13 molecules contain 13 x 2 = 26 atoms of O.

Q74. How many atoms of O are present in 15 molecules of CO2?

A) 2
B) 15
C) 17
D) 30

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CO2 has 2 atom(s) of O.

15 molecules contain 15 x 2 = 30 atoms of O.

Q75. How many atoms of H are present in 18 molecules of C6H12O6?

A) 18
B) 12
C) 30
D) 216

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of C6H12O6 has 12 atom(s) of H.

18 molecules contain 18 x 12 = 216 atoms of H.

Q76. How many atoms of H are present in 12 molecules of H2O?

A) 12
B) 2
C) 14
D) 24

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 2 atom(s) of H.

12 molecules contain 12 x 2 = 24 atoms of H.

Q77. How many atoms of H are present in 11 molecules of NH3?

A) 33
B) 14
C) 3
D) 11

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

11 molecules contain 11 x 3 = 33 atoms of H.

Q78. How many atoms of H are present in 10 molecules of H2SO4?

A) 10
B) 2
C) 20
D) 12

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 2 atom(s) of H.

10 molecules contain 10 x 2 = 20 atoms of H.

Q79. How many atoms of O are present in 12 molecules of CO2?

A) 2
B) 24
C) 14
D) 12

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CO2 has 2 atom(s) of O.

12 molecules contain 12 x 2 = 24 atoms of O.

Q80. How many atoms of O are present in 3 molecules of CO2?

A) 3
B) 2
C) 5
D) 6

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CO2 has 2 atom(s) of O.

3 molecules contain 3 x 2 = 6 atoms of O.

Q81. How many atoms of H are present in 3 molecules of NH3?

A) 6
B) 9
C) 10
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

3 molecules contain 3 x 3 = 9 atoms of H.

Q82. How many atoms of Cl are present in 3 molecules of CaCl2?

A) 5
B) 3
C) 2
D) 6

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of CaCl2 has 2 atom(s) of Cl.

3 molecules contain 3 x 2 = 6 atoms of Cl.

Q83. How many atoms of H are present in 7 molecules of H2O?

A) 7
B) 14
C) 2
D) 9

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 2 atom(s) of H.

7 molecules contain 7 x 2 = 14 atoms of H.

Q84. How many atoms of O are present in 2 molecules of H2O?

A) 3
B) 2
C) 1
D) 4

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

2 molecules contain 2 x 1 = 2 atoms of O.

Q85. How many atoms of O are present in 8 molecules of H2O?

A) 1
B) 10
C) 8
D) 9

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2O has 1 atom(s) of O.

8 molecules contain 8 x 1 = 8 atoms of O.

Q86. How many atoms of H are present in 2 molecules of NH3?

A) 2
B) 5
C) 6
D) 3

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of NH3 has 3 atom(s) of H.

2 molecules contain 2 x 3 = 6 atoms of H.

Q87. How many atoms of O are present in 17 molecules of H2SO4?

A) 4
B) 17
C) 68
D) 21

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 4 atom(s) of O.

17 molecules contain 17 x 4 = 68 atoms of O.

Q88. How many atoms of O are present in 13 molecules of H2SO4?

A) 52
B) 4
C) 13
D) 17

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of H2SO4 has 4 atom(s) of O.

13 molecules contain 13 x 4 = 52 atoms of O.

Q89. How many atoms of O are present in 15 molecules of Ca(OH)2?

A) 2
B) 17
C) 30
D) 15

Difficulty: Easy · Topic: Counting atoms in molecules

Solution

Each molecule of Ca(OH)2 has 2 atom(s) of O.

15 molecules contain 15 x 2 = 30 atoms of O.

Q90. In a balanced chemical equation, the symbol '(aq)' represents:

Difficulty: Easy-Medium · Topic: Writing Chemical Equations

Solution

'(aq)' stands for aqueous, meaning the substance is dissolved in water. Other state symbols are (s) for solid, (l) for liquid, and (g) for gas.

Q91. What is the balanced equation for the reaction of hydrogen gas with oxygen gas to form water?

Difficulty: Easy-Medium · Topic: Balancing Chemical Equations

Solution

Step 1: Write unbalanced equation: H₂ + O₂ → H₂O

Step 2: Oxygen has 2 atoms on the left but only 1 on the right. Place coefficient 2 before H₂O: H₂ + O₂ → 2H₂O

Step 3: Now hydrogen has 4 atoms on the right but 2 on the left. Place coefficient 2 before H₂: 2H₂ + O₂ → 2H₂O

Check: H: 4 = 4 ✓, O: 2 = 2 ✓

Q92. The reaction CaO + H₂O → Ca(OH)₂ is an example of:

Difficulty: Easy-Medium · Topic: Types of Chemical Reactions

Solution

In this reaction, two substances (calcium oxide and water) combine to form a single product (calcium hydroxide or slaked lime). This is the definition of a combination reaction. This reaction is also highly exothermic — the mixture becomes very hot.

Q93. Which type of reaction is represented by: 2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)?

Difficulty: Easy-Medium · Topic: Types of Chemical Reactions

Solution

A single compound (ferrous sulphate) breaks down into multiple products on heating. This is a thermal decomposition reaction. The green crystals of FeSO₄·7H₂O first lose water (turn white), then decompose to give a reddish-brown solid (Fe₂O₃) and two gases.

Q94. Electrolysis of water is a:

Difficulty: Easy-Medium · Topic: Types of Chemical Reactions

Solution

2H₂O(l) →^electricity 2H₂(g) + O₂(g)

A single compound (water) is broken into simpler substances (hydrogen and oxygen) using electrical energy. This is an electrolytic decomposition reaction.

Q95. In the reaction CuO + H₂ → Cu + H₂O, which substance is oxidised?

Difficulty: Easy-Medium · Topic: Oxidation and Reduction

Solution

H₂ gains oxygen to form H₂O. Gaining oxygen is oxidation. Therefore, H₂ is oxidised. Conversely, CuO loses oxygen to form Cu, so CuO is reduced.

Q96. Chips manufacturers fill the bags with nitrogen gas to:

Difficulty: Easy-Medium · Topic: Corrosion and Rancidity

Solution

Nitrogen is an unreactive gas. Flushing chip packets with nitrogen prevents the oxidation (rancidity) of fats and oils present in the chips, keeping them fresh for a longer time.

Q97. Which of the following conditions is NOT required for rusting of iron?

Difficulty: Easy-Medium · Topic: Corrosion and Rancidity

Solution

Rusting requires both oxygen and moisture (water). Nitrogen is an inert gas and does not participate in rusting. In fact, nitrogen atmosphere prevents rusting.

Q98. The reaction in which two compounds exchange their ions is called:

Difficulty: Easy-Medium · Topic: Types of Chemical Reactions

Solution

In a double displacement reaction, two compounds exchange their ions (or radicals) to form two new compounds. General form: AB + CD → AD + CB. Example: AgNO₃(aq) + NaCl(aq) → AgCl(s)↓ + NaNO₃(aq)

Q99. Balance the chemical equation: C + O2 -> CO2. Give coefficients in order.

A) 2, 1, 2
B) 1, 2, 1
C) 1, 1, 1
D) 2, 2, 1

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: C + O2 -> CO2

Coefficients: 1, 1, 1

Q100. Balance the chemical equation: Mg + O2 -> MgO. Give coefficients in order.

A) 1, 2, 2
B) 1, 1, 1
C) 2, 1, 2
D) 2, 2, 2

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: Mg + O2 -> MgO

Coefficients: 2, 1, 2

Q101. Balance the chemical equation: CH4 + O2 -> CO2 + H2O. Give coefficients in order.

A) 1, 1, 1, 1
B) 1, 2, 1, 2
C) 1, 3, 1, 2
D) 2, 2, 2, 2

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: CH4 + O2 -> CO2 + H2O

Coefficients: 1, 2, 1, 2

Q102. Balance the chemical equation: H2 + O2 -> H2O. Give coefficients in order.

A) 2, 1, 2
B) 1, 2, 2
C) 2, 2, 2
D) 1, 1, 1

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: H2 + O2 -> H2O

Coefficients: 2, 1, 2

Q103. Balance the chemical equation: Na + H2O -> NaOH + H2. Give coefficients in order.

A) 1, 2, 1, 1
B) 1, 1, 1, 1
C) 2, 1, 2, 1
D) 2, 2, 2, 1

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: Na + H2O -> NaOH + H2

Coefficients: 2, 2, 2, 1

Q104. Balance the chemical equation: Fe + O2 -> Fe2O3. Give coefficients in order.

A) 2, 3, 1
B) 4, 3, 2
C) 4, 2, 2
D) 1, 1, 1

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: Fe + O2 -> Fe2O3

Coefficients: 4, 3, 2

Q105. Balance the chemical equation: N2 + H2 -> NH3. Give coefficients in order.

A) 1, 3, 2
B) 1, 2, 2
C) 2, 3, 2
D) 1, 1, 2

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: N2 + H2 -> NH3

Coefficients: 1, 3, 2

Q106. Balance the chemical equation: Ca + O2 -> CaO. Give coefficients in order.

A) 1, 2, 1
B) 1, 1, 1
C) 2, 2, 2
D) 2, 1, 2

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: Ca + O2 -> CaO

Coefficients: 2, 1, 2

Q107. Balance the chemical equation: P4 + O2 -> P4O10. Give coefficients in order.

A) 1, 5, 1
B) 2, 5, 2
C) 1, 10, 1
D) 4, 5, 4

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: P4 + O2 -> P4O10

Coefficients: 1, 5, 1

Q108. Balance the chemical equation: Al + O2 -> Al2O3. Give coefficients in order.

A) 4, 2, 2
B) 4, 3, 2
C) 2, 1, 1
D) 2, 3, 1

Difficulty: Easy-Medium · Topic: Balancing chemical equations

Solution

Balancing: Al + O2 -> Al2O3

Coefficients: 4, 3, 2

Q109. Find the molar mass of CaCO3.

A) 84 g/mol
B) 110 g/mol
C) 100 g/mol
D) 60 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of CaCO3: sum of atomic masses of constituent atoms.

Molar mass = 100 g/mol

Q110. Find the molar mass of HCl.

A) 35 g/mol
B) 36.5 g/mol
C) 72 g/mol
D) 37 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of HCl: sum of atomic masses of constituent atoms.

Molar mass = 36.5 g/mol

Q111. Find the molar mass of NaCl.

A) 58.5 g/mol
B) 23 g/mol
C) 35.5 g/mol
D) 57 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of NaCl: sum of atomic masses of constituent atoms.

Molar mass = 58.5 g/mol

Q112. Find the molar mass of KMnO4.

A) 142 g/mol
B) 175 g/mol
C) 158 g/mol
D) 119 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of KMnO4: sum of atomic masses of constituent atoms.

Molar mass = 158 g/mol

Q113. Find the molar mass of NH3.

A) 15 g/mol
B) 17 g/mol
C) 31 g/mol
D) 14 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of NH3: sum of atomic masses of constituent atoms.

Molar mass = 17 g/mol

Q114. Find the molar mass of CO2.

A) 48 g/mol
B) 32 g/mol
C) 44 g/mol
D) 28 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of CO2: sum of atomic masses of constituent atoms.

Molar mass = 44 g/mol

Q115. Find the molar mass of H2O.

A) 20 g/mol
B) 18 g/mol
C) 10 g/mol
D) 16 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of H2O: sum of atomic masses of constituent atoms.

Molar mass = 18 g/mol

Q116. Find the molar mass of NaOH.

A) 40 g/mol
B) 24 g/mol
C) 38 g/mol
D) 41 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of NaOH: sum of atomic masses of constituent atoms.

Molar mass = 40 g/mol

Q117. Find the molar mass of C6H12O6.

A) 168 g/mol
B) 144 g/mol
C) 192 g/mol
D) 180 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of C6H12O6: sum of atomic masses of constituent atoms.

Molar mass = 180 g/mol

Q118. Which metal will displace the other from its salt solution: Pb or Cu?

A) Pb (more reactive, displaces the other)
B) Both equally
C) Neither
D) Cu (less reactive, cannot displace)

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Pb is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Pb (more reactive, displaces the other)

Q119. Which metal will displace the other from its salt solution: Zn or Cu?

A) Both equally
B) Neither
C) Zn (more reactive, displaces the other)
D) Cu (less reactive, cannot displace)

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Zn is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Zn (more reactive, displaces the other)

Q120. Which metal will displace the other from its salt solution: Zn or Fe?

A) Fe (less reactive, cannot displace)
B) Zn (more reactive, displaces the other)
C) Neither
D) Both equally

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Zn is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Zn (more reactive, displaces the other)

Q121. Which metal will displace the other from its salt solution: Al or Fe?

A) Fe (less reactive, cannot displace)
B) Both equally
C) Neither
D) Al (more reactive, displaces the other)

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Al is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Al (more reactive, displaces the other)

Q122. Which metal will displace the other from its salt solution: Cu or Fe?

A) Cu (less reactive, cannot displace)
B) Neither
C) Fe (more reactive, displaces the other)
D) Both equally

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Fe is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Fe (more reactive, displaces the other)

Q123. Which metal will displace the other from its salt solution: Ag or Cu?

A) Neither
B) Cu (more reactive, displaces the other)
C) Both equally
D) Ag (less reactive, cannot displace)

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Cu is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Cu (more reactive, displaces the other)

Q124. Which metal will displace the other from its salt solution: Fe or Cu?

A) Cu (less reactive, cannot displace)
B) Neither
C) Both equally
D) Fe (more reactive, displaces the other)

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Fe is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Fe (more reactive, displaces the other)

Q125. Which metal will displace the other from its salt solution: Cu or Ag?

A) Ag (less reactive, cannot displace)
B) Both equally
C) Cu (more reactive, displaces the other)
D) Neither

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Cu is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Cu (more reactive, displaces the other)

Q126. Which metal will displace the other from its salt solution: Na or Mg?

A) Na (more reactive, displaces the other)
B) Neither
C) Both equally
D) Mg (less reactive, cannot displace)

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Na is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Na (more reactive, displaces the other)

Q127. Find the percentage of O in H2O.

A) 112.5%
B) 800.0%
C) 11.11%
D) 88.89%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of O in H2O = 16 g

Molar mass of H2O = 18 g/mol

% of O = (16/18) x 100 = 88.89%

Q128. Find the percentage of Na in NaCl.

A) 60.68%
B) 64.79%
C) 39.32%
D) 254.35%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of Na in NaCl = 23 g

Molar mass of NaCl = 58.5 g/mol

% of Na = (23/58.5) x 100 = 39.32%

Q129. Find the percentage of O in CO2.

A) 27.27%
B) 266.67%
C) 72.73%
D) 137.5%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of O in CO2 = 32 g

Molar mass of CO2 = 44 g/mol

% of O = (32/44) x 100 = 72.73%

Q130. Find the percentage of H in H2O.

A) 88.89%
B) 11.11%
C) 12.5%
D) 900.0%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of H in H2O = 2 g

Molar mass of H2O = 18 g/mol

% of H = (2/18) x 100 = 11.11%

Q131. Find the percentage of Ca in CaCO3.

A) 60.0%
B) 40.0%
C) 250.0%
D) 66.67%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of Ca in CaCO3 = 40 g

Molar mass of CaCO3 = 100 g/mol

% of Ca = (40/100) x 100 = 40.0%

Q132. Find the percentage of N in NH3.

A) 121.43%
B) 466.67%
C) 17.65%
D) 82.35%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of N in NH3 = 14 g

Molar mass of NH3 = 17 g/mol

% of N = (14/17) x 100 = 82.35%

Q133. Find the percentage of C in CO2.

A) 37.5%
B) 366.67%
C) 27.27%
D) 72.73%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of C in CO2 = 12 g

Molar mass of CO2 = 44 g/mol

% of C = (12/44) x 100 = 27.27%

Q134. Find the percentage of S in H2SO4.

A) 67.35%
B) 48.48%
C) 32.65%
D) 306.25%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of S in H2SO4 = 32 g

Molar mass of H2SO4 = 98 g/mol

% of S = (32/98) x 100 = 32.65%

Q135. Find the percentage of Fe in Fe2O3.

A) 70.0%
B) 142.86%
C) 30.0%
D) 233.33%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of Fe in Fe2O3 = 112 g

Molar mass of Fe2O3 = 160 g/mol

% of Fe = (112/160) x 100 = 70.0%

Q136. Name the compound with the structural formula: CH3-CHO

A) Ethanol
B) Propanal
C) Methanol
D) Ethanal

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH3-CHO is named: Ethanal

Named based on IUPAC nomenclature rules for carbon compounds.

Q137. Name the compound with the structural formula: CH3-COOH

A) Ethanol
B) Methanoic acid
C) Ethanal
D) Ethanoic acid

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH3-COOH is named: Ethanoic acid

Named based on IUPAC nomenclature rules for carbon compounds.

Q138. Name the compound with the structural formula: CH(triple)CH

A) Ethane
B) Propyne
C) Ethene
D) Ethyne

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH(triple)CH is named: Ethyne

Named based on IUPAC nomenclature rules for carbon compounds.

Q139. Name the compound with the structural formula: CH3-CH2-CH2-OH

A) Butanol
B) Ethanol
C) Propan-2-ol
D) Propan-1-ol

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH3-CH2-CH2-OH is named: Propan-1-ol

Named based on IUPAC nomenclature rules for carbon compounds.

Q140. Name the compound with the structural formula: CH2=CH2

A) Ethane
B) Ethyne
C) Propene
D) Ethene

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH2=CH2 is named: Ethene

Named based on IUPAC nomenclature rules for carbon compounds.

Q141. Name the compound with the structural formula: HCOOH

A) Ethanoic acid
B) Methanal
C) Methanoic acid
D) Methanol

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound HCOOH is named: Methanoic acid

Named based on IUPAC nomenclature rules for carbon compounds.

Q142. Name the compound with the structural formula: CH3-OH

A) Ethanol
B) Methanol
C) Methane
D) Methanal

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH3-OH is named: Methanol

Named based on IUPAC nomenclature rules for carbon compounds.

Q143. Name the compound with the structural formula: CH3-CH2-CH3

A) Ethane
B) Butane
C) Propene
D) Propane

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH3-CH2-CH3 is named: Propane

Named based on IUPAC nomenclature rules for carbon compounds.

Q144. Name the compound with the structural formula: CH3-CH2-OH

A) Ethanoic acid
B) Ethanal
C) Methanol
D) Ethanol

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH3-CH2-OH is named: Ethanol

Named based on IUPAC nomenclature rules for carbon compounds.

Q145. What is the ester formed when propanoic acid reacts with methanol (CH3OH) in the presence of an acid catalyst?

A) Propanol
B) Methyl propanoate
C) Propanone
D) Ethyl propanoate

Difficulty: Easy-Medium · Topic: Esterification reaction

Solution

Esterification: Acid + Alcohol -> Ester + Water

propanoic acid + methanol (CH3OH) -> Methyl propanoate + H2O

Q146. What is the ester formed when methanoic acid (HCOOH) reacts with methanol (CH3OH) in the presence of an acid catalyst?

A) Ethyl ethanoate
B) Methyl methanoate (HCOOCH3)
C) Methane
D) Formaldehyde

Difficulty: Easy-Medium · Topic: Esterification reaction

Solution

Esterification: Acid + Alcohol -> Ester + Water

methanoic acid (HCOOH) + methanol (CH3OH) -> Methyl methanoate (HCOOCH3) + H2O

Q147. What is the ester formed when ethanoic acid (CH3COOH) reacts with ethanol (C2H5OH) in the presence of an acid catalyst?

A) Ethyl ethanoate (CH3COOC2H5)
B) Methyl methanoate
C) Sodium ethanoate
D) Ethanol + water only

Difficulty: Easy-Medium · Topic: Esterification reaction

Solution

Esterification: Acid + Alcohol -> Ester + Water

ethanoic acid (CH3COOH) + ethanol (C2H5OH) -> Ethyl ethanoate (CH3COOC2H5) + H2O

Q148. What is the ester formed when methanoic acid (HCOOH) reacts with ethanol (C2H5OH) in the presence of an acid catalyst?

A) Ethyl methanoate (HCOOC2H5)
B) Methyl ethanoate
C) Methanol
D) Ethanal

Difficulty: Easy-Medium · Topic: Esterification reaction

Solution

Esterification: Acid + Alcohol -> Ester + Water

methanoic acid (HCOOH) + ethanol (C2H5OH) -> Ethyl methanoate (HCOOC2H5) + H2O

Q149. What is the ester formed when ethanoic acid (CH3COOH) reacts with methanol (CH3OH) in the presence of an acid catalyst?

A) Ethanol
B) Ethyl ethanoate
C) Methyl ethanoate (CH3COOCH3)
D) Methanoic acid

Difficulty: Easy-Medium · Topic: Esterification reaction

Solution

Esterification: Acid + Alcohol -> Ester + Water

ethanoic acid (CH3COOH) + methanol (CH3OH) -> Methyl ethanoate (CH3COOCH3) + H2O

Q150. What type of bond is present in MgO? (Hint: formed between a metal and non-metal)

A) Ionic bond
B) Metallic bond
C) Covalent bond
D) Coordinate bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

MgO is Ionic bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q151. What type of bond is present in CO2? (Hint: formed between two non-metals)

A) Hydrogen bond
B) Ionic bond
C) Metallic bond
D) Covalent bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

CO2 is Covalent bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q152. What type of bond is present in NH3? (Hint: formed between two non-metals)

A) Van der Waals
B) Covalent bond
C) Ionic bond
D) Metallic bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

NH3 is Covalent bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q153. What type of bond is present in HCl? (Hint: formed between two non-metals)

A) Covalent bond
B) Metallic bond
C) Ionic bond
D) Coordinate bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

HCl is Covalent bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q154. What type of bond is present in H2O? (Hint: formed between two non-metals)

A) Van der Waals
B) Covalent bond
C) Metallic bond
D) Ionic bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

H2O is Covalent bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q155. What type of bond is present in CaCl2? (Hint: formed between a metal and non-metal)

A) Ionic bond
B) Metallic bond
C) Hydrogen bond
D) Covalent bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

CaCl2 is Ionic bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q156. What type of bond is present in NaCl? (Hint: formed between a metal and non-metal)

A) Ionic bond
B) Metallic bond
C) Hydrogen bond
D) Covalent bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

NaCl is Ionic bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q157. What type of bond is present in Na2O? (Hint: formed between a metal and non-metal)

A) Ionic bond
B) Van der Waals
C) Metallic bond
D) Covalent bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

Na2O is Ionic bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q158. What type of bond is present in CH4? (Hint: formed between two non-metals)

A) Metallic bond
B) Hydrogen bond
C) Ionic bond
D) Covalent bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

CH4 is Covalent bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q159. During electrolysis of acidified water, what is produced at the anode?

A) Chlorine gas
B) Water
C) Oxygen gas (O2)
D) Hydrogen gas

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of acidified water:

At the anode: Oxygen gas (O2)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q160. During electrolysis of molten NaCl, what is produced at the anode?

A) Chlorine gas (Cl2)
B) Oxygen gas
C) Hydrogen gas
D) Sodium metal

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of molten NaCl:

At the anode: Chlorine gas (Cl2)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q161. During electrolysis of CuSO4 solution with Cu electrodes, what is produced at the cathode?

A) Hydrogen gas
B) Sulphur
C) Oxygen gas
D) Copper metal (Cu deposited)

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of CuSO4 solution with Cu electrodes:

At the cathode: Copper metal (Cu deposited)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q162. During electrolysis of CuSO4 solution with Cu electrodes, what is produced at the anode?

A) Sulphur
B) Copper dissolves from anode (Cu -> Cu2+)
C) Oxygen gas
D) Hydrogen gas

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of CuSO4 solution with Cu electrodes:

At the anode: Copper dissolves from anode (Cu -> Cu2+)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q163. During electrolysis of acidified water, what is produced at the cathode?

A) Nothing
B) Oxygen gas
C) Chlorine gas
D) Hydrogen gas (H2)

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of acidified water:

At the cathode: Hydrogen gas (H2)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q164. During electrolysis of brine (NaCl solution), what is produced at the cathode?

A) Sodium metal
B) Hydrogen gas (H2)
C) Chlorine gas
D) Oxygen gas

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of brine (NaCl solution):

At the cathode: Hydrogen gas (H2)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q165. During electrolysis of dilute H2SO4, what is produced at the cathode?

A) Hydrogen gas (H2)
B) Sulphur dioxide
C) Water
D) Oxygen gas

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of dilute H2SO4:

At the cathode: Hydrogen gas (H2)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q166. During electrolysis of brine (NaCl solution), what is produced at the anode?

A) Oxygen gas
B) Hydrogen gas
C) Chlorine gas (Cl2)
D) Sodium metal

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of brine (NaCl solution):

At the anode: Chlorine gas (Cl2)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q167. During electrolysis of molten NaCl, what is produced at the cathode?

A) Hydrogen gas
B) Sodium metal (Na)
C) Oxygen gas
D) Chlorine gas

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of molten NaCl:

At the cathode: Sodium metal (Na)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q168. Find the molar mass of H2SO4.

A) 98 g/mol
B) 64 g/mol
C) 100 g/mol
D) 96 g/mol

Difficulty: Easy-Medium · Topic: Molar mass calculation

Solution

Molar mass of H2SO4: sum of atomic masses of constituent atoms.

Molar mass = 98 g/mol

Q169. Which metal will displace the other from its salt solution: Mg or Zn?

A) Zn (less reactive, cannot displace)
B) Mg (more reactive, displaces the other)
C) Neither
D) Both equally

Difficulty: Easy-Medium · Topic: Metal reactivity and displacement

Solution

In the reactivity series, Mg is more reactive.

A more reactive metal displaces a less reactive one from its salt solution.

Answer: Mg (more reactive, displaces the other)

Q170. Find the percentage of O in Fe2O3.

A) 333.33%
B) 70.0%
C) 30.0%
D) 42.86%

Difficulty: Easy-Medium · Topic: Percentage composition of element in compound

Solution

Mass of O in Fe2O3 = 48 g

Molar mass of Fe2O3 = 160 g/mol

% of O = (48/160) x 100 = 30.0%

Q171. Name the compound with the structural formula: CH3-CO-CH3

A) Propanal
B) Propanone (Acetone)
C) Propanol
D) Butanone

Difficulty: Easy-Medium · Topic: Naming carbon compounds

Solution

The compound CH3-CO-CH3 is named: Propanone (Acetone)

Named based on IUPAC nomenclature rules for carbon compounds.

Q172. What type of bond is present in KBr? (Hint: formed between a metal and non-metal)

A) Covalent bond
B) Metallic bond
C) Ionic bond
D) Coordinate bond

Difficulty: Easy-Medium · Topic: Ionic vs covalent bond type

Solution

KBr is Ionic bond.

Ionic bonds form between metals and non-metals (electron transfer).

Covalent bonds form between non-metals (electron sharing).

Q173. During electrolysis of dilute H2SO4, what is produced at the anode?

A) Hydrogen gas
B) Sulphur dioxide
C) Sulphuric acid
D) Oxygen gas (O2)

Difficulty: Easy-Medium · Topic: Products of electrolysis

Solution

During electrolysis of dilute H2SO4:

At the anode: Oxygen gas (O2)

Cations move to cathode (reduction), anions move to anode (oxidation).

Q174. Balance the equation: Fe₂O₃ + Al → Al₂O₃ + Fe. What are the correct coefficients (in order)?

Difficulty: Medium · Topic: Balancing Chemical Equations

Solution

Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

Check: Fe: 2 = 2 ✓, O: 3 = 3 ✓, Al: 2 = 2 ✓

This is the thermite reaction, used for welding railway tracks.

Q175. When lead nitrate solution is mixed with potassium iodide solution, a yellow precipitate is formed. This is an example of:

Difficulty: Medium · Topic: Types of Chemical Reactions

Solution

Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s)↓ + 2KNO₃(aq)

The lead and potassium ions exchange partners (double displacement). The yellow PbI₂ is insoluble and separates as a precipitate (precipitation reaction).

Q176. In the displacement reaction Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s), what happens to the colour of the solution?

Difficulty: Medium · Topic: Types of Chemical Reactions

Solution

Copper sulphate solution is blue due to Cu²⁺ ions. When zinc displaces copper (zinc is more reactive), Cu²⁺ ions are removed from solution and deposited as reddish-brown metallic copper. The ZnSO₄ solution formed is colourless, so the blue colour fades.

Q177. In the reaction MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂, which substance acts as the oxidising agent?

Difficulty: Medium · Topic: Oxidation and Reduction

Solution

MnO₂ gets reduced (Mn goes from +4 to +2 oxidation state). The substance that gets reduced is the oxidising agent because it causes the oxidation of HCl (Cl⁻ is oxidised to Cl₂).

Q178. Balance the following chemical equation and identify the type of reaction: Na + H₂O → NaOH + H₂

Difficulty: Medium · Topic: Balancing Chemical Equations

Solution

Step 1: List atoms on each side:

Unbalanced: Na + H₂O → NaOH + H₂
Na: 1 = 1, O: 1 = 1, H: 2 ≠ 3

Step 2: Balance hydrogen by placing coefficient 2 before NaOH and H₂O:

Na + 2H₂O → 2NaOH + H₂

H: 4 = 4 ✓, but Na: 1 ≠ 2

Step 3: Balance Na by placing coefficient 2 before Na:

2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

Check: Na: 2=2 ✓, H: 4=4 ✓, O: 2=2 ✓

Type: This is a displacement reaction — sodium displaces hydrogen from water.

Q179. What is a decomposition reaction? Give three examples of decomposition reactions triggered by different forms of energy.

Difficulty: Medium · Topic: Types of Chemical Reactions

Solution

Definition: A decomposition reaction is a chemical reaction in which a single compound breaks down into two or more simpler products.

Examples:

1. Thermal decomposition (by heat):

CaCO₃(s) →^Δ CaO(s) + CO₂(g)

Limestone (calcium carbonate) decomposes on heating to form quicklime and carbon dioxide.

2. Electrolytic decomposition (by electricity):

2H₂O(l) →^electricity 2H₂(g) + O₂(g)

Water decomposes into hydrogen and oxygen when an electric current is passed through it.

3. Photolytic decomposition (by sunlight):

2AgCl(s) →^sunlight 2Ag(s) + Cl₂(g)

Silver chloride (white) turns grey in sunlight as it decomposes into silver and chlorine. This principle is used in black-and-white photography.

Q180. Define oxidation and reduction in terms of gain or loss of oxygen. Identify the substance oxidised and the substance reduced in the following reaction: ZnO + C → Zn + CO

Difficulty: Medium · Topic: Oxidation and Reduction

Solution

Oxidation: Gain of oxygen by a substance.

Reduction: Loss of oxygen by a substance.

In the reaction: ZnO + C → Zn + CO

ZnO is reduced — it loses oxygen to become Zn.
C (carbon) is oxidised — it gains oxygen to become CO.

ZnO is the oxidising agent (it provides oxygen to carbon).

Carbon is the reducing agent (it removes oxygen from ZnO).

This is a redox reaction because oxidation and reduction occur simultaneously.

Q181. What is rancidity? List three methods to prevent rancidity in food items.

Difficulty: Medium · Topic: Corrosion and Rancidity

Solution

Rancidity: When fats and oils in food are oxidised by exposure to air, they develop an unpleasant smell and taste. This process is called rancidity.

Methods to prevent rancidity:

Adding antioxidants: Chemicals like BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) are added to food products to prevent oxidation.
Flushing with nitrogen: Chip packets and other snack packets are filled with nitrogen gas (an unreactive gas) to displace oxygen and prevent rancidity.
Storing in airtight containers: Reducing exposure to air slows down oxidation of fats.

Other methods: Refrigeration (low temperature slows oxidation), storing in the dark (light accelerates rancidity).

Q182. Balance the equation: Al + HCl → AlCl₃ + H₂. What is the sum of all coefficients in the balanced equation?

Difficulty: Medium · Topic: Balancing Chemical Equations

Solution

Unbalanced: Al + HCl → AlCl₃ + H₂

Step 1: Balance Cl — 1 on left, 3 on right. Place 3 before HCl:

Al + 3HCl → AlCl₃ + H₂

Step 2: Balance H — 3 on left, 2 on right. LCM of 3 and 2 is 6. Place 6 before HCl:

Al + 6HCl → AlCl₃ + H₂

Step 3: Now Cl = 6 on left, need 6 on right. Place 2 before AlCl₃:

Al + 6HCl → 2AlCl₃ + H₂

Step 4: Balance Al — 1 on left, 2 on right. Place 2 before Al:

2Al + 6HCl → 2AlCl₃ + H₂

Step 5: Balance H — 6 on left, 2 on right. Place 3 before H₂:

2Al + 6HCl → 2AlCl₃ + 3H₂

Check: Al: 2=2 ✓, H: 6=6 ✓, Cl: 6=6 ✓

Sum of coefficients: 2 + 6 + 2 + 3 = 13

Note: The correct answer is 13.

Q183. When the equation Fe₃O₄ + H₂ → Fe + H₂O is balanced, the coefficient of H₂O is:

Difficulty: Medium · Topic: Balancing Chemical Equations

Solution

Balanced equation: Fe₃O₄ + 4H₂ → 3Fe + 4H₂O

Check: Fe: 3=3 ✓, O: 4=4 ✓, H: 8=8 ✓

The coefficient of H₂O is 4.

Q184. Explain why silver articles turn black when exposed to air for a long time. Write the relevant chemical equation.

Difficulty: Medium · Topic: Corrosion and Rancidity

Solution

Air contains traces of hydrogen sulphide (H₂S) gas, especially in polluted environments. Silver reacts with H₂S in the presence of moisture to form a black coating of silver sulphide:

2Ag(s) + H₂S(g) → Ag₂S(s) + H₂(g)

The Ag₂S is black, which is why silver jewellery, utensils, and idols lose their shine over time. This is a form of corrosion (also called tarnishing). Silver articles can be cleaned using baking soda paste or professional silver polish.

Q185. In a redox reaction, the substance that gets reduced is called:

Difficulty: Medium · Topic: Oxidation and Reduction

Solution

The substance that gets reduced (gains electrons / loses oxygen) itself causes the oxidation of the other substance. Therefore, it is called the oxidising agent.

Conversely, the substance that gets oxidised is called the reducing agent.

Q186. Find the oxidation number of N in HNO3.

A) -3
B) +4
C) +3
D) +5

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In HNO3, let oxidation number of N = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of N = +5

Q187. Find the oxidation number of Cr in K2Cr2O7.

A) +4
B) +6
C) +7
D) +3

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In K2Cr2O7, let oxidation number of Cr = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of Cr = +6

Q188. Find the oxidation number of N in NH3.

A) -1
B) +3
C) -3
D) 0

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In NH3, let oxidation number of N = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of N = -3

Q189. Find the oxidation number of C in CO2.

A) +4
B) +2
C) +6
D) -4

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In CO2, let oxidation number of C = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of C = +4

Q190. Find the oxidation number of Fe in Fe2O3.

A) +2
B) +6
C) 0
D) +3

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In Fe2O3, let oxidation number of Fe = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of Fe = +3

Q191. Find the oxidation number of Mn in KMnO4.

A) +5
B) +6
C) +4
D) +7

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In KMnO4, let oxidation number of Mn = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of Mn = +7

Q192. Find the oxidation number of P in H3PO4.

A) -3
B) +4
C) +5
D) +3

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In H3PO4, let oxidation number of P = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of P = +5

Q193. Find the oxidation number of Cl in HClO4.

A) +3
B) -1
C) +5
D) +7

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In HClO4, let oxidation number of Cl = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of Cl = +7

Q194. Find the oxidation number of S in Na2SO3.

A) +6
B) -2
C) +4
D) +2

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In Na2SO3, let oxidation number of S = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of S = +4

Q195. Find the oxidation number of S in H2SO4.

A) -2
B) +6
C) +2
D) +4

Difficulty: Medium · Topic: Oxidation number of an element

Solution

In H2SO4, let oxidation number of S = x.

Using the rule that sum of oxidation numbers = 0 for neutral compound:

Oxidation number of S = +6

Q196. 10 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 5600.0
B) 5601.0
C) 2800.0
D) 5.6

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 10/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 5600.0 mL

Q197. 20 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 6.89
B) 6893.3
C) 6892.3
D) 3446.2

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 20/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 6892.3 mL

Q198. 40 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 22400.0
B) 11200.0
C) 22.4
D) 22401.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 40/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 22400.0 mL

Q199. 10 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 1723.1
B) 3.45
C) 3447.2
D) 3446.2

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 10/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 3446.2 mL

Q200. 40 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 13785.6
B) 6892.3
C) 13784.6
D) 13.78

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 40/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 13784.6 mL

Q201. 5 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 1724.1
B) 1723.1
C) 861.5
D) 1.72

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 5/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 1723.1 mL

Q202. 65 g of Mg reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Mg = 24 g/mol, molar volume = 22400 mL at STP)

A) 30333.3
B) 60.67
C) 60666.7
D) 60667.7

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Mg = 65/24

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 60666.7 mL

Q203. 27 g of Al reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Al = 27 g/mol, molar volume = 22400 mL at STP)

A) 22400.0
B) 33600.0
C) 11200.0
D) 33.6

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Al = 27/27

Moles of H2 = moles of metal x 3/2

Volume at STP = moles x 22400 mL = 33600.0 mL

Q204. 30 g of Mg reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Mg = 24 g/mol, molar volume = 22400 mL at STP)

A) 28.0
B) 14000.0
C) 28000.0
D) 28001.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Mg = 30/24

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 28000.0 mL

Q205. 13 g of Mg reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Mg = 24 g/mol, molar volume = 22400 mL at STP)

A) 12134.3
B) 12.13
C) 12133.3
D) 6066.7

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Mg = 13/24

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 12133.3 mL

Q206. 40 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 16000.0
B) 8000.0
C) 16.0
D) 16001.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 40/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 16000.0 mL

Q207. 13 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 4481.0
B) 2240.0
C) 4.48
D) 4480.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 13/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 4480.0 mL

Q208. 27 g of Mg reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Mg = 24 g/mol, molar volume = 22400 mL at STP)

A) 25201.0
B) 25200.0
C) 12600.0
D) 25.2

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Mg = 27/24

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 25200.0 mL

Q209. 10 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 4000.0
B) 4001.0
C) 2000.0
D) 4.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 10/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 4000.0 mL

Q210. 30 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 10339.5
B) 10.34
C) 5169.2
D) 10338.5

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 30/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 10338.5 mL

Q211. 30 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 16801.0
B) 16800.0
C) 8400.0
D) 16.8

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 30/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 16800.0 mL

Q212. 30 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 12001.0
B) 6000.0
C) 12.0
D) 12000.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 30/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 12000.0 mL

Q213. 10 g of Mg reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Mg = 24 g/mol, molar volume = 22400 mL at STP)

A) 9.33
B) 4666.7
C) 9333.3
D) 9334.3

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Mg = 10/24

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 9333.3 mL

Q214. 50 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 10000.0
B) 20000.0
C) 20001.0
D) 20.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 50/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 20000.0 mL

Q215. 50 g of Mg reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Mg = 24 g/mol, molar volume = 22400 mL at STP)

A) 46667.7
B) 46666.7
C) 46.67
D) 23333.3

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Mg = 50/24

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 46666.7 mL

Q216. 65 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 11200.0
B) 22.4
C) 22400.0
D) 22401.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 65/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 22400.0 mL

Q217. 27 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 10800.0
B) 10801.0
C) 5400.0
D) 10.8

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 27/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 10800.0 mL

Q218. 24 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 13440.0
B) 13.44
C) 13441.0
D) 6720.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 24/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 13440.0 mL

Q219. 65 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 13000.0
B) 26.0
C) 26000.0
D) 26001.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 65/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 26000.0 mL

Q220. 40 g of Al reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Al = 27 g/mol, molar volume = 22400 mL at STP)

A) 49.78
B) 16592.6
C) 33185.2
D) 49777.8

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Al = 40/27

Moles of H2 = moles of metal x 3/2

Volume at STP = moles x 22400 mL = 49777.8 mL

Q221. 20 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 8.0
B) 4000.0
C) 8001.0
D) 8000.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 20/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 8000.0 mL

Q222. 13 g of Al reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Al = 27 g/mol, molar volume = 22400 mL at STP)

A) 16.18
B) 16177.8
C) 10785.2
D) 5392.6

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Al = 13/27

Moles of H2 = moles of metal x 3/2

Volume at STP = moles x 22400 mL = 16177.8 mL

Q223. 24 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 4135.4
B) 8271.8
C) 8270.8
D) 8.27

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 24/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 8270.8 mL

Q224. 13 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 3640.0
B) 7280.0
C) 7281.0
D) 7.28

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 13/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 7280.0 mL

Q225. 13 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 5.2
B) 5201.0
C) 5200.0
D) 2600.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 13/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 5200.0 mL

Q226. 65 g of Al reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Al = 27 g/mol, molar volume = 22400 mL at STP)

A) 53925.9
B) 80888.9
C) 80.89
D) 26963.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Al = 65/27

Moles of H2 = moles of metal x 3/2

Volume at STP = moles x 22400 mL = 80888.9 mL

Q227. 5 g of Fe reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Fe = 56 g/mol, molar volume = 22400 mL at STP)

A) 1000.0
B) 2000.0
C) 2.0
D) 2001.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Fe = 5/56

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 2000.0 mL

Q228. 20 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 11201.0
B) 11200.0
C) 5600.0
D) 11.2

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 20/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 11200.0 mL

Q229. 65 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 36400.0
B) 36401.0
C) 36.4
D) 18200.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 65/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 36400.0 mL

Q230. 40 g of Mg reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Mg = 24 g/mol, molar volume = 22400 mL at STP)

A) 37333.3
B) 37334.3
C) 37.33
D) 18666.7

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Mg = 40/24

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 37333.3 mL

Q231. 5 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 2800.0
B) 1400.0
C) 2.8
D) 2801.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 5/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 2800.0 mL

Q232. 50 g of Al reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Al = 27 g/mol, molar volume = 22400 mL at STP)

A) 20740.7
B) 62222.2
C) 62.22
D) 41481.5

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Al = 50/27

Moles of H2 = moles of metal x 3/2

Volume at STP = moles x 22400 mL = 62222.2 mL

Q233. 30 g of Al reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Al = 27 g/mol, molar volume = 22400 mL at STP)

A) 37.33
B) 12444.4
C) 24888.9
D) 37333.3

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Al = 30/27

Moles of H2 = moles of metal x 3/2

Volume at STP = moles x 22400 mL = 37333.3 mL

Q234. 50 g of Ca reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Ca = 40 g/mol, molar volume = 22400 mL at STP)

A) 28001.0
B) 28.0
C) 14000.0
D) 28000.0

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Ca = 50/40

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 28000.0 mL

Q235. 50 g of Zn reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Zn = 65 g/mol, molar volume = 22400 mL at STP)

A) 17.23
B) 17230.8
C) 17231.8
D) 8615.4

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Zn = 50/65

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 17230.8 mL

Q236. 5 g of Mg reacts with excess dilute HCl. Find the volume of H2 produced at STP. (Atomic mass of Mg = 24 g/mol, molar volume = 22400 mL at STP)

A) 4.67
B) 4667.7
C) 4666.7
D) 2333.3

Difficulty: Medium · Topic: Volume of H2 from metal-acid reaction at STP

Solution

Moles of Mg = 5/24

Moles of H2 = moles of metal x 2/2

Volume at STP = moles x 22400 mL = 4666.7 mL

Q237. Explain why decomposition reactions are considered the opposite of combination reactions. Support your answer with one example of each.

Difficulty: Medium-Hard · Topic: Types of Chemical Reactions

Solution

Combination reaction: Two or more reactants combine to form a single product.

Example: CaO(s) + H₂O(l) → Ca(OH)₂(aq)

Here, quicklime and water combine to form a single product — slaked lime.

Decomposition reaction: A single reactant breaks down into two or more simpler products.

Example: Ca(OH)₂(s) →^Δ CaO(s) + H₂O(g)

Here, slaked lime decomposes into quicklime and water vapour on strong heating.

Why they are opposites: The product of the combination reaction (calcium hydroxide) is the reactant in the decomposition reaction. Combination builds up complexity; decomposition breaks it down. Combination reactions are generally exothermic (release energy), while decomposition reactions are generally endothermic (absorb energy).

Q238. A student claims that all displacement reactions are also redox reactions. Do you agree? Justify with an example.

Difficulty: Medium-Hard · Topic: Types of Chemical Reactions

Solution

Yes, the claim is correct.

In a displacement reaction, a more reactive element takes the place of a less reactive element. This inherently involves electron transfer:

Example: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Zn loses 2 electrons → Zn²⁺ (oxidation)
Cu²⁺ gains 2 electrons → Cu (reduction)

Since oxidation and reduction occur simultaneously, every displacement reaction is a redox reaction. Zinc is the reducing agent and Cu²⁺ is the oxidising agent.

Q239. Which of the following reactions is an example of an exothermic combination reaction?

Difficulty: Medium-Hard · Topic: Types of Chemical Reactions

Solution

Burning of natural gas (methane) involves carbon and hydrogen combining with oxygen to form CO₂ and H₂O, releasing a large amount of heat. This makes it both a combination and an exothermic reaction.

Options B and C are endothermic decomposition reactions. Option D is an endothermic dissolution.

Q240. A white salt on heating decomposes to give brown fumes and a yellow residue. The yellow residue turns white on cooling. Identify the salt and write the balanced chemical equation for the reaction.

Difficulty: Hard · Topic: Types of Chemical Reactions

Solution

Identification: The salt is lead nitrate — Pb(NO₃)₂.

Evidence:

Brown fumes = NO₂ (nitrogen dioxide gas)
Yellow residue = PbO (lead oxide) — PbO is yellow when hot and turns white/pale yellow on cooling

Balanced equation:

2Pb(NO₃)₂(s) →^Δ 2PbO(s) + 4NO₂(g) + O₂(g)

This is a thermal decomposition reaction. This is a classic NCERT activity (Activity 1.5) used to demonstrate decomposition by heat.

Reaction Type	Balanced Equation
Combination	2Mg(s) + O₂(g) → 2MgO(s)
Combination	CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
Thermal Decomposition	2FeSO₄(s) →^Δ Fe₂O₃(s) + SO₂(g) + SO₃(g)
Thermal Decomposition	CaCO₃(s) →^Δ CaO(s) + CO₂(g)
Electrolytic Decomposition	2H₂O(l) →^electricity 2H₂(g) + O₂(g)
Photolytic Decomposition	2AgBr(s) →^sunlight 2Ag(s) + Br₂(g)
Displacement	Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
Displacement	Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
Double Displacement	Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s)↓ + 2KNO₃(aq)
Redox	CuO(s) + H₂(g) → Cu(s) + H₂O(l)
Rusting	4Fe(s) + 3O₂(g) + xH₂O → 2Fe₂O₃·xH₂O

Chapter 1: Chemical Reactions and Equations

Important Formulas

Solved Questions

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