Question

Which of the following causes the rusting of iron?
1. Oxidation
2. Reduction
3. Chemical Reaction with Oxygen
4. Chemical Reaction with $C{O_2}$
A) 1 and 2
B) 2 and 3
C) 3 and 4
D) 1 and 3

Answer 1

Rusting of iron is a chemical change, which refers to the formation of rust, or mixture of iron oxides, on the surface of iron objects. The rust is formed as a result of redox reaction between iron and oxygen in a moist environment (air containing high levels of moisture).

Complete answer:
Rust on the surface of iron is formed by exposure of iron to oxygen in presence of moisture. The oxygen bonds with the iron atoms, resulting in the formation of iron oxides. This only happens in the presence of moisture and air. The presence of air and water vapour are thus necessary conditions for rusting. Oxygen acts as a very good oxidising agent and iron is a reducing agent, the iron atom thus readily gives electrons when exposed to oxygen. The reaction can be given as: $Fe \to F{e^{ + 2}} + 2{e^ - }$
The process of rusting is increased with the presence of water. We have observed that iron rusts faster in sea water. The presence of salt makes the process of rusting even faster. Rust is made up of various iron oxides namely Iron (II) oxide or ferrous oxide and Iron (III) oxide or Ferric oxide.
Thus, the causes for the rusting of iron are: Oxidation and Chemical Reaction with Oxygen. The correct answer is Option (D) 1 and 3.

Note:
Rusting causes the iron to become flaky, thus degrading its strength, appearance and permeability. The desirable properties of iron are not found in a rusted iron. Rusting can damage automobiles, railings, grills and other iron structures also.