Acid rain is primarily caused by air pollution.

Air Pollution: Acid rain is a type of environmental pollution that is primarily caused by emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. These pollutants are released into the air through various human activities, including the burning of fossil fuels such as coal, oil, and natural gas in industrial processes, power plants, and vehicles.

Sulfur Dioxide (SO2): Sulfur dioxide is released into the atmosphere when fossil fuels containing sulfur, like coal and oil, are burned. It can also come from natural sources such as volcanic eruptions. In the atmosphere, SO2 can react with other compounds and form sulfuric acid (H2SO4), a major component of acid rain.

Nitrogen Oxides (NOx): Nitrogen oxides, which are generated when combustion occurs at high temperatures, are another significant contributor to acid rain. These compounds can combine with other atmospheric components to form nitric acid (HNO3), another component of acid rain.

THEREFORE THE CORRECT OPTION IS [1].