Explain phenomenon of acid rain.

Burning of fossil fuels release oxides of Sulphur, and nitrogen into the air. Nitogen gets oxidized and forms its oxides. These chemicals combine with water and fall as acid rain on earth. The pH of this rain water is less than 5. Acid rain reacts with metals & corrodes them, also it reacts with calcium containing substances, therby producing gypsum which then flakes off.