Iron sheets are coated with a substance to prevent them from rusting:
(A) Coating on the iron sheet is zinc
(B) The process of covering iron with zinc is called 'galvanisation'
(C) Rusting takes place in the presence of moisture but absence of air
(D) Rusting is a 'reduction' reaction
Choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) and (B) only
Rusting is the slow oxidation of iron: iron reacts with oxygen of the air and water (moisture) to form hydrated iron(III) oxide, the reddish-brown rust. Coating the iron keeps air and water away from it.
(A) Coating on the iron sheet is zinc Correct. Iron sheets are coated with zinc; zinc is more reactive than iron, so it corrodes first and protects the iron even where the coating is scratched.
(B) The process of covering iron with zinc is called 'galvanisation' Correct. Depositing a thin layer of zinc on iron or steel is galvanisation; galvanised sheets are used for roofs, buckets and pipes.
(C) Rusting takes place in the presence of moisture but absence of air Incorrect. Rusting needs both air (oxygen) and moisture; iron kept in dry air or in boiled water with no dissolved air does not rust.
(D) Rusting is a 'reduction' reaction Incorrect. In rusting, iron gains oxygen and loses electrons, so it is an oxidation reaction, not reduction.