Explain the following phenomenon (i) Acid rain (ii) Ozone depletion (iii) Global warming or green house effect.

(i) Acid Rain. The oxides of nitrogen and sulphur present in air as pollutant get dissolved in rain water to form nitric acid and sulphuric acid respectively. The presence of these makes the rain acidic. The acid rain damages monuments, statues and buildings. It also causes gradual degradation of soil and a decline in forest and agricultural productivity.

(ii) Ozone depletion. Reduction in thickness of ozone layer or holes in the ozone layer of atmosphere is known as depletion of ozone. Depletion of ozone layer is mainly caused by Chlorofluorocarbons (CFCs). (CFCs) are used in refrigerators, fire extinguishers and aerosol sprayers. These break the ozone molecules and lead to its depletion. Due to depletion of ozone layer, more UV radiation reaches the earth and causes skin cancer, damage to eyes and immune system. 

(iii) Global warming or Green house effect. Certain gases such as CO₂ and CH₄ (methane) when present in sufficient amount trap the heat of the sun and increase the temperature of the Earth. This increase in temperature of earth is known as global warming and the phenomenon is called green house effect. 
Global warming may cause :

(i) melting of ice caps of mountains and glaciers resulting in floods and rise in sea level.

(ii) variation in weather.