What causes acid rain?

The phenomenon of acid rain primarily results from the complex chemical reactions involving sulfur dioxide (SO2) and nitrogen oxides (NOx) with water and other atmospheric chemicals. When sulfur dioxide is emitted into the atmosphere, often from burning fossil fuels, it can react with water vapor, oxygen, and other trace chemicals to form sulfuric acid. Similarly, nitrogen oxides can also react, leading to the formation of nitric acid. These acids then mix with precipitation (rain, snow, etc.), resulting in acid rain, which can have detrimental effects on the environment, such as damaging forests, harming aquatic life, and eroding buildings.

This understanding clarifies why the other options do not correctly represent the primary causes of acid rain. The first choice cites methane, which is unrelated to acid rain formation. The second option suggests a mixing of gases but lacks the detailed chemical context that defines acid rain. The third choice refers to carbon dioxide, which can contribute to environmental issues like climate change, but it does not lead to the acidity in rain that is characteristic of acid rain. Hence, the identified correct answer encompasses the critical reactions and components responsible for this environmental concern.