International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

How do nitrogen oxides and sulfur dioxide contribute to acid rain?

1. They react with oxygen in the atmosphere

2. They combine with water in the atmosphere to form acidic solutions

3. They release energy when dissolved in water

4. They precipitate as solids in water

The correct answer is: They combine with water in the atmosphere to form acidic solutions

Nitrogen oxides and sulfur dioxide contribute to acid rain primarily through their ability to combine with water in the atmosphere, creating acidic solutions. When these gases are released into the atmosphere, they can react with water vapor, oxygen, and other chemicals. In the case of sulfur dioxide, it reacts with water to form sulfurous acid (H₂SO₃), and in the presence of oxygen, it can further oxidize to form sulfuric acid (H₂SO₄). Similarly, nitrogen oxides can react with water and oxygen to produce nitric acid (HNO₃). Both sulfuric acid and nitric acid significantly lower the pH of rainwater, making it acidic, which is then referred to as acid rain. Understanding the role of these gases in contributing to acid rain underscores the importance of atmospheric chemistry and environmental science. The other choices do not accurately describe the mechanism by which nitrogen oxides and sulfur dioxide lead to acid rain, focusing instead on processes that aren't directly responsible for the formation of acid rain.