Acid rain is primarily caused by the emission of sulfur and nitrogen oxides. Which of the following reactions correctly represents the formation of sulfuric acid in the atmosphere?

Solution

1. Atmospheric sulfur dioxide is oxidized by oxygen or ozone: $2{\text{SO}}_2+{\text{O}}_2\to 2{\text{SO}}_3$.
2. Sulfur trioxide is highly reactive with water vapor in the atmosphere.
3. The reaction is ${\text{SO}}_3+{\text{H}}_2\text{O}\to {\text{H}}_2{\text{SO}}_4$.
4. This process contributes significantly to the acidity of rain.
5. Hence the answer is (A).