Which of the following gases does not cause acid rain ?

Options

A. Sulphur dioxide
B. Methane
C. Nitrous oxide
D. Carbon monoxide

Answer

To determine which gas does not cause acid rain, we need to analyze the gases listed in the question: sulfur dioxide, methane, nitrous oxide, and carbon monoxide.

### Step-by-Step Solution:

1. **Understanding Acid Rain**: Acid rain is formed when certain gases react with water in the atmosphere, leading to the formation of acids that fall as precipitation. The primary gases responsible for acid rain are sulfur dioxide (SO2) and nitrogen oxides (NOx).

2. **Analyzing Sulfur Dioxide (SO2)**:
- Sulfur dioxide is produced during the combustion of fossil fuels.
- When SO2 combines with water vapor in the atmosphere, it forms sulfuric acid (H2SO4).
- Therefore, sulfur dioxide contributes to acid rain.

3. **Analyzing Nitrous Oxide (NO)**:
- Nitrous oxide is emitted from various sources, including vehicle emissions.
- It can be oxidized in the atmosphere to form nitrogen dioxide (NO2), which then reacts with water to form nitric acid (HNO3).
- Thus, nitrous oxide also contributes to acid rain.

4. **Analyzing Methane (CH4)**:
- Methane is a greenhouse gas and is not directly associated with acid rain.
- While it can have toxic effects, it does not react with water to form acids that contribute to acid rain.
- Therefore, methane does not cause acid rain.

5. **Analyzing Carbon Monoxide (CO)**:
- Carbon monoxide is produced from incomplete combustion of fossil fuels.
- It does not react with water to form any acids.
- Therefore, carbon monoxide does not contribute to acid rain.

6. **Conclusion**: Among the gases listed, methane and carbon monoxide do not cause acid rain. However, since methane is primarily a greenhouse gas and does not contribute to acid formation, it is the best answer to the question.

### Final Answer:
**Methane (CH4)** does not cause acid rain.

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