Which of these is a clean source of energy?

Options

A. Petrol
B. Coal
C. Wind
D. Wood

Explanation

### Step-by-Step Solution:

1. **Identify the Options**: The question asks us to determine which of the given options is a clean source of energy. The options include petrol, coal, wind energy, and wood.

2. **Analyze Each Option**:
- **Petrol**:
- Petrol is derived from crude oil, which is a fossil fuel.
- When burned, petrol emits smoke and pollutants, contributing to air pollution.
- **Coal**:
- Coal is also a fossil fuel.
- Burning coal releases a significant amount of smoke and particulate matter, leading to pollution.
- **Wind Energy**:
- Wind energy is harnessed using windmills.
- It does not produce any emissions or pollutants during energy production, making it environmentally friendly.
- **Wood**:
- Wood is often used for cooking and heating, especially in rural areas.
- Burning wood releases smoke and other pollutants, contributing to air pollution.

3. **Determine the Clean Source**:
- After analyzing all the options, it is clear that wind energy is the only option that does not cause pollution and is considered a clean source of energy.

4. **Conclusion**:
- Therefore, the clean source of energy among the options given is **wind energy**.