Question

: What conditions are required for rusting to take place?
A.Water only
B.Oxygen only
C.Water and oxygen
D.Water and carbon dioxide

Answer 1

Hint: Rust is the iron oxide, reddish brown in colour that forms on the surface of the iron once it is left exposed to the atmosphere for a long time. The iron gets oxidised in the air.

Complete step by step answer:
When the surface of iron is exposed to the atmospheric oxygen and water in the form of either liquid or gaseous water vapour then the surface gets coated with a reddish brown layer of iron-oxides due to the reaction between the surface of the iron with the oxygen and water vapour present in the medium. For this reaction to take place, both water and oxygen are required as can be seen in the reaction given below:
$$4Fe+n{H}_{2}O+3O_2\to 2F{e}_2{O}_3.n{H}_{2}O$$
Where $$2F{e}_2{O}_3.n{H}_{2}O$$ is the rust or hydrated iron oxide.

So, as both oxygen and water are required for the formation of the rust, the correct answer is option C.

Note:
Rusting is an example of an oxidation-reduction reaction in which iron reacts with water and oxygen to form hydrated iron oxides. Due to this problem, iron is alloyed with different other elements to form the steel. There are different types of steel, among which, the “stainless” steel does not get rusted. It has carbon, sulphur, titanium, aluminium, nickel, copper, silicon, selenium, niobium, and molybdenum. The best way to reduce rusting to coat the iron surface with a layer of zinc called “galvanization”.