Examples of corrosion include
(A) Rusting of iron
(B) Tarnishing of silver
(C) Green coating on copper and bronze
(D) Zinc coating on iron
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B) and (C) only
Corrosion is the slow destruction of a metal by its surroundings: air, moisture and other gases convert the surface of the metal into its oxide or other salts. It is an electrochemical process in which the metal is oxidised.
(A) Rusting of iron — Correct. Iron is oxidised by oxygen in the presence of moisture to hydrated iron(III) oxide, rust:
\( \displaystyle \ce{4Fe + 3O2 + 2xH2O -> 2Fe2O3.xH2O} \)
(B) Tarnishing of silver — Correct. Silver reacts with traces of sulphur compounds in air to form a black film of silver sulphide, \( \ce{Ag2S} \).
(C) Green coating on copper and bronze — Correct. Copper reacts with oxygen, moisture and carbon dioxide to form a green layer of basic copper carbonate, \( \ce{CuCO3.Cu(OH)2} \).
(D) Zinc coating on iron — Incorrect. Coating iron with zinc is galvanisation, a method of preventing corrosion. Zinc is more reactive than iron, so it is oxidised in preference and protects the iron even when the coating is scratched.
NCERT (2026-27 edition):
Corrosion
Corrosion – “… Prevention of corrosion is of prime importance. … Another simple method is to cover the surface by other metals (Sn, Zn, etc.) that are inert or react to save the object.”