Q51. Black colour on silver is due to:
A. Oxide ❌
B. Sulphide ✅
C. Chloride ❌
D. Nitrate ❌
Why correct: Silver reacts with sulphur to form black silver sulphide.
Why others wrong: Oxide, chloride and nitrate do not cause black colour.
Q52. Green colour on copper forms due to:
A. Oxide ❌
B. Carbonate ✅
C. Chloride ❌
D. Sulphide ❌
Why correct: Copper forms green copper carbonate.
Why others wrong: These do not form green coating.
Q53. Rusting needs:
A. Oxygen only ❌
B. Water only ❌
C. Both oxygen and moisture ✅
D. Carbon dioxide ❌
Why correct: Both air and water are required for rusting.
Why others wrong: One alone is not enough.
Q54. Corrosion is slow destruction of metals due to:
A. Acids, moisture, air ✅
B. Heat only ❌
C. Cold only ❌
D. Pressure ❌
Why correct: All environmental factors cause corrosion.
Why others wrong: Alone they cannot corrode metal.
Q55. Rancidity is oxidation of:
A. Proteins ❌
B. Minerals ❌
C. Fats and oils ✅
D. Water ❌
Why correct: Fats react with oxygen and spoil.
Why others wrong: Rancidity happens only in fats.
Q56. Similar reactions show:
A. Neutralization ❌
B. Redox ✅
C. Precipitation ❌
D. Decomposition ❌
Why correct: Oxidation and reduction occur together.
Why others wrong: They do not include both processes.
Q57. Fe₂O₃ + Al reaction is called:
A. Thermite reaction ✅
B. Corrosion ❌
C. Decomposition ❌
D. Neutralisation ❌
Why correct: Aluminium replaces iron violently.
Why others wrong: They describe other processes.
Q58. Reduction is gaining:
A. Oxygen ❌
B. Hydrogen ✅
C. Nitrogen ❌
D. Carbon ❌
Why correct: Reduction means hydrogen gain.
Why others wrong: Oxygen gain is oxidation.
Q59. Oxidation is losing:
A. Hydrogen ✅
B. Carbon ❌
C. Nitrogen ❌
D. Sulphur ❌
Why correct: Loss of hydrogen = oxidation.
Why others wrong: They are not definitions.
Q60. Balanced equations ensure:
A. Equal heat ❌
B. Equal pressure ❌
C. Equal atoms ✅
D. Equal colour ❌
Why correct: Same number of atoms on both sides.
Why others wrong: Balance is about atoms only.
Q61. Law used is:
A. Boyle ❌
B. Avogadro ❌
C. Conservation of mass ✅
D. Charles ❌
Why correct: Matter is neither created nor destroyed.
Why others wrong: Gas laws are different.
Q62. PbO is:
A. Oxidised ❌
B. Reduced ✅
C. Neutralised ❌
D. Decomposed ❌
Why correct: PbO loses oxygen.
Why others wrong: No acid-base or breakdown.
Q63. Carbon is:
A. Reduced ❌
B. Oxidised ✅
C. Neutral ❌
D. Displaced ❌
Why correct: Carbon gains oxygen.
Why others wrong: No displacement or neutrality.
Q64. Which is oxidizing agent?
A. Pb ❌
B. CO₂ ❌
C. PbO ✅
D. C ❌
Why correct: Gives oxygen for oxidation.
Why others wrong: They do not oxidise others.
Q65. Which is reducing agent?
A. PbO ❌
B. C ✅
C. Pb ❌
D. CO₂ ❌
Why correct: Carbon removes oxygen.
Why others wrong: They do not reduce.
Q66. NH₃ formation is:
A. Combination ✅
B. Displacement ❌
C. Decomposition ❌
D. Precipitation ❌
Why correct: Two substances combine.
Why others wrong: These do not fit.
Q67. H₂S burning is:
A. Oxidation ✅
B. Reduction ❌
C. Displacement ❌
D. Decomposition ❌
Why correct: Oxygen is gained.
Why others wrong: No replacement or breakdown.
Q68. BaCl₂ + Al₂(SO₄)₃ is:
A. Single displacement ❌
B. Double displacement ✅
C. Decomposition ❌
D. Combination ❌
Why correct: Ions exchange.
Why others wrong: No single replacement.
Q69. Potassium with water is:
A. Neutralisation ❌
B. Combination ❌
C. Oxidation ❌
D. Displacement ✅
Why correct: Potassium replaces hydrogen.
Why others wrong: No acid-base or just oxidation.
Q70. Hydrogen formed is due to:
A. Reduction ✅
B. Oxidation ❌
C. Electrolysis ❌
D. Precipitation ❌
Why correct: Hydrogen ions gain electrons.
Why others wrong: No electricity or solids.
Q71. Rusting is:
A. Fast ❌
B. Slow ✅
C. Instant ❌
D. Explosive ❌
Why correct: Happens gradually.
Why others wrong: It is not rapid.
Q72. Corrosion damages:
A. Metals ✅
B. Plastics ❌
C. Rubber ❌
D. Wood ❌
Why correct: Only metals corrode.
Why others wrong: They decay differently.
Q73. Rancidity spoils:
A. Iron ❌
B. Oil ✅
C. Glass ❌
D. Plastic ❌
Why correct: Oil contains fats.
Why others wrong: Rancidity occurs in fats.
Q74. Rancidity changed smell due to:
A. Reduction ❌
B. Oxidation ✅
C. Heating ❌
D. Cooling ❌
Why correct: Oxygen reaction produces bad smell.
Why others wrong: Not due to temperature.
Q75. Airtight containers prevent:
A. Rusting ❌
B. Oxidation ✅
C. Heating ❌
D. Melting ❌
Why correct: No oxygen enters.
Why others wrong: They do not affect heat or melting.
Q76. Food preservatives often are:
A. Oxidants ❌
B. Antioxidants ✅
C. Reductants ❌
D. Salts ❌
Why correct: Prevent oxidation.
Why others wrong: Not main function.
Q77. Oxidation always involves:
A. Oxygen ❌
B. Hydrogen ❌
C. Gain or loss concept ✅
D. Heat always ❌
Why correct: Electron transfer concept is key.
Why others wrong: Oxygen is not always involved.
Q78. Reduction never involves:
A. Gain of O ✅
B. Loss of O ❌
C. Gain of H ❌
D. No oxygen ❌
Why correct: Gaining oxygen is oxidation.
Why others wrong: They define reduction.
Q79. Which is not corrosion?
A. Rusting ❌
B. Tarnishing ❌
C. Burning ✅
D. Green coating ❌
Why correct: Burning is combustion, not corrosion.
Why others wrong: They are corrosion forms.
Q80. Corrosion is:
A. Useful ❌
B. Harmful ✅
C. Beneficial ❌
D. Harmless ❌
Why correct: Causes damage.
Why others wrong: It destroys material.
Q81. Metals react with:
A. Plastic ❌
B. Moisture ✅
C. Paper ❌
D. Glass ❌
Why correct: Moisture causes corrosion.
Why others wrong: Not reactive.
Q82. Zinc coating on iron prevents:
A. Rancidity ❌
B. Corrosion ✅
C. Reduction ❌
D. Oxidation of copper ❌
Why correct: Zinc protects iron.
Why others wrong: Unrelated.
Q83. Green colour on copper is commonly called:
A. Rust ❌
B. Patina ✅
C. Tarnish ❌
D. Oxide ❌
Why correct: Green coating is patina.
Why others wrong: Rust is for iron.
Q84. Tarnishing is corrosion of:
A. Iron ❌
B. Silver ✅
C. Zinc ❌
D. Aluminium ❌
Why correct: Silver forms sulphide.
Why others wrong: Tarnishing name is specific.
Q85. Magnesium burns bright because:
A. Heat ❌
B. Oxygen ❌
C. Oxidation ✅
D. Reduction ❌
Why correct: Magnesium oxidises rapidly.
Why others wrong: No reduction here.
Q86. Oxidation happens in:
A. Air ✅
B. Water ❌
C. Vacuum ❌
D. Space ❌
Why correct: Oxygen is in air.
Why others wrong: No oxygen present.
Q87. Gains hydrogen means:
A. Oxidised ❌
B. Reduced ✅
C. Neutral ❌
D. Displaced ❌
Why correct: Hydrogen gain = reduction.
Why others wrong: Opposite of oxidation.
Q88. Loses hydrogen means:
A. Reduced ❌
B. Oxidised ✅
C. Neutralised ❌
D. Displaced ❌
Why correct: Hydrogen loss = oxidation.
Why others wrong: Not reduction.
Q89. Substance attacking metals include:
A. Oxygen ❌
B. Moisture ❌
C. Acids ❌
D. All ✅
Why correct: All cause corrosion.
Why others wrong: Each alone is incomplete.
Q90. Loss of shiny surface is due to:
A. Cleaning ❌
B. Corrosion ✅
C. Polishing ❌
D. Painting ❌
Why correct: Tarnishing removes shine.
Why others wrong: They improve appearance.
Q91. Oxidation and reduction occur:
A. Separately ❌
B. Together ✅
C. Randomly ❌
D. Occasionally ❌
Why correct: Always simultaneous.
Why others wrong: One cannot occur alone.
Q92. NH₃ formation requires:
A. Decomposition ❌
B. Combination ✅
C. Displacement ❌
D. Redox ❌
Why correct: Two elements combine.
Why others wrong: No breaking or replacing.
Q93. Oil becomes unusable due to:
A. Reduction ❌
B. Corrosion ❌
C. Rancidity ✅
D. Evaporation ❌
Why correct: Fats oxidise and spoil.
Why others wrong: They do not affect taste.
Q94. Antioxidants prevent:
A. Spoilage ❌
B. Oxidation ❌
C. Rancidity ❌
D. Both B and C ✅
Why correct: Oxidation causes rancidity.
Why others wrong: Only partial answers.
Q95. Chips are stored in:
A. Oxygen filled bags ❌
B. Nitrogen flushed bags ✅
C. Water filled bags ❌
D. Sealed hot bags ❌
Why correct: Nitrogen prevents oxidation.
Why others wrong: Oxygen spoils food.
Q96. Rancid oil smells:
A. Pleasant ❌
B. Neutral ❌
C. Bad ✅
D. Sweet ❌
Why correct: Smell becomes foul.
Why others wrong: Oil does not smell sweet.
Q97. Rust is mainly:
A. FeO ❌
B. Fe₂O₃ ❌
C. Hydrated Fe₂O₃ ✅
D. FeCO₃ ❌
Why correct: Rust contains water.
Why others wrong: Dry oxide is not rust.
Q98. Rusting increases when:
A. Dry air ❌
B. Moist air ✅
C. Cold air ❌
D. Vacuum ❌
Why correct: Moisture speeds corrosion.
Why others wrong: Rust slows without water.
Q99. Prevent oxidation means:
A. Stop oxygen contact ✅
B. Add water ❌
C. Increase air ❌
D. Add heat ❌
Why correct: No oxygen = no oxidation.
Why others wrong: They increase damage.
Q100. Best example of corrosion is:
A. Burning paper ❌
B. Rusting iron ✅
C. Cooking food ❌
D. Melting ice ❌
Why correct: Rusting shows corrosion clearly.
Why others wrong: They are physical / chemical changes.