⚗️ Chemical Reactions and Equations – Class 10 Science MCQs

Part 3: Effects of Oxidation and Reduction Reactions – Corrosion, Rancidity, Applications (Q51–Q75)

Q51. Corrosion of iron is commonly called:

A. Rancidity
B. Rusting
C. Tarnishing
D. Galvanization

✅ Correct Answer: B. Rusting

Explanation: Rusting = formation of hydrated ferric oxide (Fe₂O₃·xH₂O) on iron.

Q52. Which conditions are necessary for rusting of iron?

A. Air (oxygen) only
B. Water only
C. Both air (oxygen) and water
D. Neither air nor water

✅ Correct Answer: C. Both air (oxygen) and water

Q53. The reddish-brown coating formed on iron objects is:

A. FeSO₄
B. Fe₂O₃·xH₂O
C. Fe₃O₄
D. FeCl₃

✅ Correct Answer: B. Fe₂O₃·xH₂O

Q54. Rusting is a type of:

A. Reduction
B. Oxidation
C. Both oxidation and reduction
D. Neutralization

✅ Correct Answer: C. Both oxidation and reduction

Explanation: Iron is oxidized to Fe²⁺, oxygen reduced to OH⁻ → redox process.

Q55. Which method does NOT prevent rusting of iron?

A. Galvanization
B. Painting
C. Oiling/greasing
D. Heating in air

✅ Correct Answer: D. Heating in air

Explanation: Heating actually accelerates oxidation.

Q56. Galvanization is coating iron with:

A. Copper
B. Zinc
C. Silver
D. Aluminium

✅ Correct Answer: B. Zinc

Q57. The black coating formed on silver is due to:

A. Ag₂O
B. Ag₂S
C. AgCl
D. AgNO₃

✅ Correct Answer: B. Ag₂S

Q58. Green layer formed on copper is due to:

A. CuSO₄
B. Basic copper carbonate
C. CuO
D. CuCl₂

✅ Correct Answer: B. Basic copper carbonate (CuCO₃·Cu(OH)₂)

Q59. Which reaction is responsible for rancidity in food?

A. Reduction of oils
B. Oxidation of fats and oils
C. Fermentation of oils
D. Hydrolysis of proteins

✅ Correct Answer: B. Oxidation of fats and oils

Q60. Which of these is a sign of rancidity?

A. Foul smell in food
B. Change in taste
C. Change in colour
D. All of these

✅ Correct Answer: D. All of these

Q61. Rancidity can be prevented by:

A. Storing food in air-tight containers
B. Adding antioxidants
C. Refrigeration
D. All of these

✅ Correct Answer: D. All of these

Q62. Which of the following is used as an antioxidant in food?

A. Sodium benzoate
B. Butylated hydroxytoluene (BHT)
C. Common salt
D. Baking soda

✅ Correct Answer: B. Butylated hydroxytoluene (BHT)

Q63. Keeping food in nitrogen atmosphere prevents rancidity because:

A. Nitrogen reacts with fats
B. Nitrogen displaces oxygen
C. Nitrogen cools the food
D. Nitrogen dissolves fats

✅ Correct Answer: B. Nitrogen displaces oxygen

Q64. Corrosion of aluminium is less harmful because:

A. Aluminium never corrodes
B. Aluminium forms a protective oxide layer
C. Aluminium is a noble metal
D. Aluminium is very reactive

✅ Correct Answer: B. Aluminium forms a protective oxide layer

Q65. The process of coating iron with zinc to prevent rusting is called:

A. Electroplating
B. Galvanization
C. Alloying
D. Painting

✅ Correct Answer: B. Galvanization

Q66. The process of coating metals with a thin layer of chromium or nickel is called:

A. Painting
B. Galvanization
C. Electroplating
D. Alloying

✅ Correct Answer: C. Electroplating

Q67. Which of the following is an example of corrosion?

A. Rusting of iron
B. Tarnishing of silver
C. Green coating on copper
D. All of these

✅ Correct Answer: D. All of these

Q68. Iron articles are painted to:

A. Increase weight
B. Improve appearance only
C. Prevent contact with air and water
D. Make them rust faster

✅ Correct Answer: C. Prevent contact with air and water

Q69. Rancidity in food items is due to:

A. Reduction reaction
B. Oxidation reaction
C. Neutralization reaction
D. Double displacement reaction

✅ Correct Answer: B. Oxidation reaction

Q70. Which is a method to delay rancidity in potato chips?

A. Keeping in sunlight
B. Storing in air-tight packets flushed with nitrogen
C. Storing with open lid
D. Mixing with water

✅ Correct Answer: B. Storing in air-tight packets flushed with nitrogen

Q71. Which type of reaction is rusting of iron?

A. Decomposition
B. Oxidation–reduction
C. Neutralization
D. Double displacement

✅ Correct Answer: B. Oxidation–reduction

Q72. Which gas is responsible for blackening of silver ornaments?

A. Oxygen
B. Sulphur dioxide (SO₂)
C. Hydrogen sulphide (H₂S)
D. Nitrogen

✅ Correct Answer: C. Hydrogen sulphide (H₂S)

Q73. Which is the most common method of preventing corrosion?

A. Using expensive alloys
B. Coating with paint, oil or grease
C. Hammering
D. Heating

✅ Correct Answer: B. Coating with paint, oil or grease

Q74. Which process is responsible for “patina” formation on copper statues?

A. Reduction
B. Oxidation + Carbonation
C. Hydrolysis
D. Neutralization

✅ Correct Answer: B. Oxidation + Carbonation (forming basic copper carbonate)

Q75. Which statement is correct about corrosion and rancidity?

A. Both are reduction reactions
B. Both are beneficial processes
C. Both are harmful oxidation processes
D. Both are neutralization processes

✅ Correct Answer: C. Both are harmful oxidation processes

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