Corrosion & Prevention — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Corrosion & Prevention MCQs with step-by-step solutions (13 questions). Part of Metals & Non-Metals. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Corrosion & Prevention · medium · theory
The rusting of iron requires the presence of both:
A. only dry air
B. only water
C. oxygen (air) and moisture (water) ✓ Correct
D. oxygen and nitrogen
Solution: Iron rusts only when both air (oxygen) and water/moisture are present.
Q2 — Corrosion & Prevention · hard · theory
Rust is chemically:
A. iron chloride
B. pure iron
C. hydrated iron(III) oxide ✓ Correct
D. iron sulphide
Solution: Rust is hydrated iron(III) oxide, Fe₂O₃·xH₂O.
Q3 — Corrosion & Prevention · medium · theory
The process of coating iron with a layer of zinc to prevent rusting is called:
A. galvanisation ✓ Correct
B. annealing
C. tempering
D. electrolysis
Solution: Galvanisation coats iron with zinc, which protects it from rusting.
Q4 — Corrosion & Prevention · medium · theory
Which of the following is NOT a method of preventing rusting?
A. Oiling and greasing
B. Galvanising
C. Painting
D. Adding salt to water ✓ Correct
Solution: Salt water actually speeds up rusting; painting, oiling and galvanising prevent it.
Q5 — Corrosion & Prevention · hard · theory
The green coating that forms on copper articles exposed to moist air is mainly:
A. copper chloride
B. iron oxide
C. basic copper carbonate ✓ Correct
D. copper sulphide
Solution: Copper corrodes to form a green layer of basic copper carbonate.
Q6 — Corrosion & Prevention · medium · theory
Stainless steel does not rust because it is an alloy of iron with:
A. copper and tin
B. carbon only
C. zinc and lead
D. chromium and nickel ✓ Correct
Solution: Adding chromium and nickel makes steel resistant to corrosion (stainless steel).
Q7 — Corrosion & Prevention · hard · theory
The black coating that dulls silver articles over time is due to the formation of:
A. silver oxide only
B. silver chloride
C. silver sulphide ✓ Correct
D. rust
Solution: Silver reacts with sulphur compounds in the air to form black silver sulphide (tarnish).
Q8 — Corrosion & Prevention · hard · theory
Iron objects rust faster near the sea because the moist air there contains:
A. no oxygen
B. no moisture
C. dissolved salts, which speed up corrosion ✓ Correct
D. only pure water
Solution: Salt-laden coastal air accelerates the electrochemical process of rusting.
Q9 — Corrosion & Prevention · easy · theory
The rusting of iron takes place only when iron is exposed to both
A. oxygen (air) and moisture (water) ✓ Correct
B. carbon dioxide and oil
C. sunlight and salt only
D. nitrogen and oil
Solution: Rusting is the slow corrosion of iron and needs both oxygen from the air and moisture (water). If either air or water is absent, iron does not rust, which is why iron kept in dry air or in boiled air-free water stays rust-free.
Q10 — Corrosion & Prevention · medium · theory
The reddish-brown flaky substance that forms on the surface of an iron object left in damp air is chemically
A. hydrated iron(III) oxide ✓ Correct
B. iron sulphide
C. copper carbonate
D. iron carbonate
Solution: Rust is chemically hydrated iron(III) oxide, that is iron oxide combined with water. It is flaky and porous, so it keeps flaking off and exposes fresh iron underneath to further rusting.
Q11 — Corrosion & Prevention · medium · theory
Iron objects are often coated with a layer of zinc in a process called galvanisation. Zinc protects the iron because
A. zinc reacts with iron to turn it into steel
B. zinc simply makes the iron heavier and stronger
C. zinc is more reactive than iron and corrodes in preference to it, protecting the iron even if the layer is scratched ✓ Correct
D. zinc is less reactive than iron and seals it completely forever
Solution: Zinc is more reactive than iron, so it corrodes first and shields the iron. Even if the zinc coating is scratched, the exposed zinc still corrodes in preference to the iron, giving sacrificial protection.
Q12 — Corrosion & Prevention · hard · theory
Aluminium is quite a reactive metal, yet aluminium articles do not corrode away and stay durable in everyday use. This is because
A. aluminium is actually one of the least reactive metals
B. aluminium never reacts with oxygen at all
C. a thin, tough layer of aluminium oxide forms on the surface and protects the metal underneath ✓ Correct
D. aluminium is always painted before it is used
Solution: Aluminium reacts quickly with oxygen to form a thin, hard, unreactive layer of aluminium oxide on its surface. This tightly stuck layer seals the metal beneath and stops further corrosion.
Q13 — Corrosion & Prevention · hard · theory
Large iron ships have blocks of magnesium or zinc bolted to their steel hulls below the waterline. The main purpose of these blocks is that they
A. are cheap decorations with no chemical role
B. being more reactive, corrode in place of the iron and so protect the hull ✓ Correct
C. make the ship float higher in the water
D. make the iron of the hull more reactive
Solution: Magnesium and zinc are more reactive than iron, so they corrode first and are eaten away instead of the hull. These sacrificial blocks are replaced from time to time and protect the iron ship from rusting.