Question

Acid rain is occur when the atmosphere is heavily polluted with-

Answer 1

Hint : Acid rain is composed of rain drops, fog with dust in them which are slightly more acidic than acidity of normal water.
As we know, the atmosphere contains a number of gases which have a tendency to get dissolved in water. Solubility of these atmospheric gases differs depending upon their chemical and physical properties.

Complete Step By Step Answer:
Acid rain is defined as “the rain water which contains different types of acid like sulphuric acid, nitric acid or carbonic acid which reduces the pH of the rain water”.
Rain water is not neutral in nature because it is not present in its pure state and hence, rain water has a pH lower than 7 which shows slight acidic nature. components of acid rain include-
carbon dioxide gas which is released into the atmosphere from vehicles, industries, burning of organic matter.
$C{O_{2\left( g \right)}} + {H_2}{O_{\left( {aq} \right)}} \to {H_2}C{O_{3\left( {aq} \right)}}$
Carbon dioxide releases combine with water vapour in the atmosphere to form carbonic acid.
sulphur dioxide gas which is released into the atmosphere from roasting fossils, coal mines, oil and diesel from automobiles.
$2S{O_{2\left( g \right)}} + {O_{2\left( g \right)}} + 2{H_2}{O_{\left( l \right)}} \to 2{H_2}S{O_{4\left( {aq} \right)}}$
Sulphur dioxide releases combine with water vapour and oxygen in the atmosphere to form sulphuric acid.
nitric oxide gas which is released into the atmosphere from automobiles, various industries, power plants.
$4N{O_{2\left( g \right)}} + {O_{2\left( g \right)}} + {H_2}{O_{\left( l \right)}} \to 4HN{O_{3\left( {aq} \right)}}$
Nitric oxide gas which is released combines with water vapour and oxygen in the atmosphere to form nitric acid.
Hence, when the atmosphere is heavily polluted with nitric acid, sulphuric acid, carbonic acid causes formation of acid rain.
During the rainfall all these gases released into the atmosphere through various sources dissolved into rain water and reduced the pH of rain water below 6.
Due to dissolution of these gases in rainfall they increase the acidity of water therefore it is known as acid rain. The average pH of acid rain ranges from 6 to 2.

Note :
pH of acid rain sometimes drops below the pH 2 which is highly toxic for the environment. This pH usually reaches the area where the pollution level of these gases is very high.
acid rain gets mixed with normal water of ponds, lakes, rivers and lowers their pH and makes them toxic for living organisms in these water bodies.
acid rain reacts with monuments of the world like Taj Mahal and causes major damages.