All the following contribute to pollution except-

Options

A. Thermal power plant
B. Automobiles
C. Nuclear power plant
D. Hydroelectric power project.

Answer

To solve the question "All the following contribute to pollution except-", we need to analyze each of the provided options to determine which one does not contribute to pollution.

### Step-by-Step Solution:

1. **Examine the First Option: Thermal Power Plant**
- Thermal power plants generate electricity by burning fossil fuels, which releases pollutants such as carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen oxides (NOx).
- **Conclusion**: Thermal power plants contribute to pollution.

2. **Examine the Second Option: Automobiles**
- Automobiles are known sources of air pollution as they emit gases like carbon dioxide (CO2), sulfur dioxide (SO2), and carbon monoxide (CO).
- **Conclusion**: Automobiles contribute to pollution.

3. **Examine the Third Option: Nuclear Power Plant**
- Nuclear power plants produce energy through nuclear reactions and release carbon dioxide (CO2) during the energy production process. They also generate radioactive waste, which is a significant environmental concern.
- **Conclusion**: Nuclear power plants contribute to pollution.

4. **Examine the Fourth Option: Hydroelectric Power Project**
- Hydroelectric power projects generate electricity by harnessing the energy of flowing water. They do not emit pollutants like CO2 or SO2 during operation and are generally considered a clean source of energy.
- **Conclusion**: Hydroelectric power projects do not contribute to pollution.

### Final Answer:
The correct answer is **hydroelectric power projects**, as they do not contribute to pollution.

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