Question

Which metals do not corrode easily?
(A) Gold
(B) Iron
(C) Aluminium
(D) Zinc

Answer 1

Hint: Corrosion is basically an electrochemical phenomenon. Corrosion is the slow formation of undesirable compounds such as oxide, sulphides or carbonates at the surface of metal by reaction with moisture and other atmospheric oxygen. A metal is oxidised by loss of electron to oxygen and forms metal oxide. The rusting of iron, the tarnishing of silver, and formation of a green coating on copper metal surfaces are some examples of corrosion.
Among given metals gold $\text{(Au)}$ present in the lowest position and aluminium $\text{(Al)}$ metal present in the highest position in electrochemical series (the arrangement of metal electrodes in the increasing order of their standard reduction potential).

Complete answer:
Metal that are placed in the top of the series are highly reactive and these metals corrode more easily in the exposure of moist air. However those metals placed at the bottom in the electrochemical series are least reactive and do not corrode easily. So, aluminium $\text{(Al)}$ forms a coating of oxide on the surface after reacting with the oxygen in the air. Gold and platinum are unreactive and do not corrode even after thousands of years.

Note:
If sodium$\text{(Na)}$ and potassium $\text{(K)}$ were not stored under oil they would corrode very rapidly. The more exposed copper roof and pipes quickly form a green coating over the surface.
Rusting is the most common form of corrosion used for the iron $\text{(Fe)}$ and steel. In the galvanization process to protect the iron from rusting, the iron metal is coated with molten zinc$\text{(Zn)}$. Since zinc metal is above the iron in electrochemical series, so corrosion of zinc metal forms a protective covering over the iron metal and prevents it from rusting.