______ is responsible for acid rain.

Options

A. Carbon dioxide
B. Sulphur dioxide
C. Carbon monoxide
D. Chloroflurocarbons

Explanation

**Step-by-Step Solution:**

1. **Understanding Acid Rain**: Acid rain occurs when rainwater becomes acidic due to the presence of certain gases in the atmosphere.

2. **Identifying Responsible Gases**: The primary gases responsible for acid rain are sulfur dioxide (SO₂) and nitrogen dioxide (NO₂).

3. **Chemical Reactions**:
- When sulfur dioxide (SO₂) is released into the atmosphere, it can react with water vapor (H₂O) to form sulfuric acid (H₂SO₄).
- Similarly, nitrogen dioxide (NO₂) can react with water vapor to form nitric acid (HNO₃).

4. **Formation of Acid Rain**: These acids mix with the water vapor in the clouds. When it rains, the acidic compounds are deposited as acid rain.

5. **Evaluating Options**:
- **Option 1: Carbon Dioxide** - This does not form an acid that leads to acid rain.
- **Option 2: Sulfur Dioxide** - This is correct as it forms sulfuric acid, contributing to acid rain.
- **Option 3: Carbon Monoxide** - This does not lead to acid formation.
- **Option 4: Chlorofluorocarbon** - This is related to ozone depletion, not acid rain.

6. **Conclusion**: The gas responsible for acid rain is **sulfur dioxide (SO₂)**.

**Final Answer**: Sulfur dioxide is responsible for acid rain.

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