Question

In which of the following the corrosion of iron will be most rapid?

• A. In pure water
• B. In pure oxygen
• C. In air and saline water
• D. Same rate of corrosion in all of the above.

Answer 1

The correct option is C In air and saline water

The corrosion of iron indicates a chemical change in the metal. Rust (hydrous oxide i.e. $F{e}_2{O}_3.x{H}_{2}O$) is an example of this change that results when the iron is exposed to water and damp air. A thin film of oxide forms on the iron which protects the metal from further corrosion by slowing the rate of oxidation.
The $N{a}^{+}\&C{l}^{-}$ present in saline water increase the conductance of the solution in contact with the metal surface. This accelerates the formation of $F{e}^{2+}$ ions and hence that of rust $F{e}_2{O}_3.x{H}_{2}O$