Anecessary ingredient for acid rain to occur is
a. air pollution
b. heat pollution
c. runoff pollution
d. water pollution

Option (a) is the correct answer.

Explanation:

Acid rain is the rainfall whose water has become acidic in nature due to the atmospheric or air pollution.

When compounds like sulfur dioxide and nitrogen oxides release into the air then there occurs a chemical reaction. When both these gases mix and react with water, oxygen and other pollutants then they rise at very high altitude into the atmosphere.

As a result rain water becomes acidic.

Thus, we can conclude that a necessary ingredient for acid rain to occur is air pollution.