Corrosion refers to the destruction or deterioration of a substance due to its interactions with the surrounding environment. Corrosion is a natural process and occurs when the substance is in contact with air, water, chemicals like acid etc. Corrosion can damage metals causing it to lose properties such as strength and conductivity of heat/electricity.

Corrosion can be prevented by various techniques like painting the surface of the material, galvanizing, oiling, greasing etc.

(a) Copper when in contact with moist carbon dioxide in air gains a green coloured coat over copper. This coat is nothing but copper carbonate formed by the reaction of copper and moist carbon dioxide.

(b) Silver reacts with sulphur present in the air to form a black coating of silver sulphide over the surface of silver.