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

What gases contribute to acid rain that are formed in car engines?

1. Carbon dioxide

2. Oxides of nitrogen

3. Sulfur dioxide

4. Methane

The correct answer is: Oxides of nitrogen

Acid rain is primarily caused by the presence of sulfuric acid and nitric acid in the atmosphere, which are formed when pollutants such as sulfur dioxide and oxides of nitrogen react with water vapor. In the context of car engines, one of the significant contributors to the formation of acid rain is the oxides of nitrogen. Car engines produce nitrogen oxides (NOx) as a byproduct of combustion, particularly at high temperatures where nitrogen from the air reacts with oxygen. These nitrogen oxides can easily mix with water in the atmosphere, leading to the formation of nitric acid. When this acid falls back to the Earth as precipitation, it contributes to the phenomenon known as acid rain. Identifying oxides of nitrogen as a contributor highlights their role in environmental issues caused by vehicle emissions, differentiating them from other gases such as carbon dioxide, which, while significant in global warming, does not contribute to acid rain. Similarly, sulfur dioxide, although relevant, is not directly produced in large quantities from car engines compared to industrial sources; therefore, it's not the best answer in this context. Methane is not related to acid rain formation at all, as it does not produce acids when reacting with atmospheric components. Thus, the focus on oxides of