Correct Option
Acid rain is primarily caused by the atmospheric reactions of sulphur dioxide (SO₂) and nitrogen oxides (NOₓ). These gases originate predominantly from anthropogenic sources, including the combustion of fossil fuels in power generation, industrial processes, and vehicular emissions. In the atmosphere, these oxides react with water vapor, oxygen, and other chemicals to form sulphuric acid (H₂SO₄) and nitric acid (HNO₃). The key chemical transformations include:
- SO₂ + H₂O → H₂SO₃
- SO₃ + H₂O → H₂SO₄
- 2NO₂ + H₂O → HNO₂ + HNO₃
These acids then dissolve in atmospheric moisture and precipitate as acid rain, leading to environmental degradation. Oxides of hydrogen, such as water (H₂O) or hydrogen peroxide (H₂O₂), are not considered primary pollutants contributing to acid rain; rather, water acts as a medium for the chemical reactions.
Incorrect Options
Option (a) is incorrect because oxides of hydrogen (e.g., H₂O, H₂O₂) do not function as primary pollutants causing acid rain. While water is crucial for the formation process, it is not an acidic pollutant in this context.
Option (b) is incorrect as it excludes oxides of nitrogen, which are major contributors to acid rain along with oxides of sulphur.
Option (d) is incorrect because it inaccurately includes oxides of hydrogen as a cause of acid rain.