Green coating on copper in rainy season is due to the formation of CuCO3.Cu(OH)2.

Explanation:
Copper is a metal that is highly reactive with oxygen and water in the atmosphere. When copper comes in contact with air and moisture, a series of chemical reactions occur, resulting in the formation of a green coating on the surface of the copper. This green coating is known as copper carbonate hydroxide or copper(II) carbonate dihydroxide, with the chemical formula CuCO3.Cu(OH)2.

The formation of the green coating on copper can be explained in the following steps:

1. Oxidation: When copper is exposed to air, it undergoes oxidation. The copper atoms lose electrons and form copper(II) ions (Cu2+). This reaction can be represented as follows:
2Cu(s) + O2(g) → 2Cu2+(aq)

2. Reaction with carbon dioxide: The copper(II) ions in the presence of carbon dioxide in the air react to form copper(II) carbonate (CuCO3). This reaction can be represented as follows:
Cu2+(aq) + CO2(g) + H2O(l) → CuCO3(s) + H2O(l)

3. Reaction with water: The copper(II) carbonate reacts with water to form copper(II) hydroxide (Cu(OH)2) and carbon dioxide. This reaction can be represented as follows:
CuCO3(s) + H2O(l) → Cu(OH)2(s) + CO2(g)

4. Formation of green coating: The copper(II) hydroxide further reacts with copper(II) carbonate to form copper carbonate hydroxide (CuCO3.Cu(OH)2), which is the green-colored compound that coats the surface of the copper. This reaction can be represented as follows:
2Cu(OH)2(s) + CuCO3(s) → CuCO3.Cu(OH)2(s) + H2O(l)

The green coating on the copper surface provides a protective layer that helps to slow down the further corrosion of copper. It acts as a barrier between the copper and the surrounding environment, preventing direct contact with moisture and oxygen. However, over time, this coating can also undergo further reactions and degrade, exposing the underlying copper to corrosion again.

In conclusion, the green coating on copper in the rainy season is due to the formation of copper carbonate hydroxide (CuCO3.Cu(OH)2), which is a result of the reactions between copper, oxygen, carbon dioxide, and water in the atmosphere.