Which of the following is the primary cause of acid rain?

Acid rain primarily occurs due to the release of sulfur dioxide (SO₂) and nitrogen oxides (NOx) into the atmosphere, which are products of combustion processes, particularly from coal-burning power plants and automobile exhaust. When these gases are emitted, they react with water vapor, oxygen, and other chemicals in the atmosphere to form sulfuric and nitric acids. These acids then mix with rainwater, resulting in precipitation that has a lower pH than normal rain, characterizing it as "acid rain."

The role of coal-burning power plants is significant, as they are major contributors to sulfur dioxide emissions. Likewise, automobiles primarily release nitrogen oxides, which further contribute to the formation of acid rain. The widespread use of these energy sources and vehicles across various regions leads to elevated levels of these pollutants, meaning that they are key factors in the generation of acid rain.

Therefore, the correct answer underscores the importance of industrial and vehicular emissions in relation to this environmental issue.