Why is sulphur dioxide considered as an air pollutant?

Options

A. It increases the temperature of the atmosphere.
B. It is used as insecticide which causes air pollution.
C. It causes acid rain due to formation of sulphuric acid on combining with `O_(2) and H_(2)O`.
D. It is a strong oxidising agent hence oxidises the other components of air.

Answer

### Step-by-Step Solution:

1. **Definition of Sulfur Dioxide**: Sulfur dioxide (SO₂) is a colorless gas with a pungent odor, commonly produced from volcanic eruptions and industrial processes, especially the burning of fossil fuels.

2. **Reactivity in the Atmosphere**: When sulfur dioxide is released into the atmosphere, it can react with oxygen (O₂) and water vapor (H₂O) present in the air.

3. **Formation of Sulfuric Acid**: The reaction between sulfur dioxide, oxygen, and water leads to the formation of sulfuric acid (H₂SO₄). The chemical reaction can be represented as:
\[ \text{SO}_2 + \text{O}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 \]

4. **Acid Rain**: The sulfuric acid formed can then mix with rainwater, resulting in acid rain. Acid rain has a lower pH than normal rainwater and can have harmful effects on the environment, including soil degradation, water body acidification, and damage to plants and aquatic life.

5. **Environmental Impact**: Due to its role in forming acid rain, sulfur dioxide is classified as an air pollutant. The acid rain can lead to various environmental issues, such as the corrosion of buildings and monuments, harm to wildlife, and negative impacts on human health.

6. **Conclusion**: Therefore, sulfur dioxide is considered an air pollutant primarily because it contributes to the formation of acid rain, which poses significant risks to the environment and human health.