Option c correct because after combustion nature gas don't left any residue ( wastes produced)

Understanding Clean Energy Sources
Clean energy sources are those that produce energy with minimal environmental impact, particularly in terms of greenhouse gas emissions and pollution. Let's evaluate the options provided:
1. Coal
- Coal is a fossil fuel that is rich in carbon.
- Burning coal releases significant amounts of carbon dioxide (CO2), sulfur dioxide (SO2), and other pollutants.
- It is one of the largest contributors to air pollution and climate change.
2. Wood
- Wood is a renewable resource; however, its classification as a clean energy source is debated.
- When burned, wood emits CO2 and other particulates, contributing to air pollution.
- Sustainable forestry practices can mitigate some environmental impacts, but the burning process still releases emissions.
3. Natural Gas
- Natural gas is considered a cleaner fossil fuel than coal and oil.
- It emits lower levels of CO2 and pollutants when burned.
- However, it is still a fossil fuel and can contribute to greenhouse gas emissions through methane leaks during extraction and transport.
Conclusion
Given the evaluations:
- (a) Coal: Not a clean energy source due to high emissions.
- (b) Wood: Somewhat renewable, but still emits pollutants when burned.
- (c) Natural Gas: Cleaner than coal and wood but still a fossil fuel.
Final Assessment
- (d) All of these: Incorrect. None of these options can be classified as clean energy sources in the true sense.
Clean energy sources generally include solar, wind, hydroelectric, and geothermal energy, which do not emit greenhouse gases during operation.