Explain the following terms with one example each:
(a) Corrosion (b) Rancidity

Explanation

Corrosion : It is the process of deterioration of a metal as a result of its reaction with air or water present in environment. Therefore, when metals are exposed to atmosphere, they react with air or water present in the environment and form undesirable compounds on their surfaces. This process is called corrosion.
Almost all metals except noble metals such as gold, platinum and palladium get corroded. For example, when iron is exposed to moisture for a long time, its surface acquires coating of a brown flaky substance called rust. Similarly, surface of copper acquires a green coating of basic copper carbonate, etc.