Natural gas is the cleanest fuel among the options provided. Here's an explanation of why natural gas is considered the cleanest fuel:

1. Composition and Characteristics:
- Natural gas is a fossil fuel composed primarily of methane (CH4), with small amounts of other hydrocarbon gases.
- It is formed underground over millions of years from the remains of plants and animals, and it is extracted through drilling.
- Natural gas is a colorless and odorless gas in its pure form.

2. Combustion Process:
- When natural gas is burned, it undergoes combustion, combining with oxygen to produce heat, water vapor, and carbon dioxide (CO2).
- The combustion of natural gas is highly efficient, releasing a significant amount of heat energy per unit of fuel burned.
- Compared to other fuels, such as coal or oil, natural gas combustion emits less carbon dioxide and other pollutants.

3. Low Emissions:
- Natural gas has the lowest carbon content of all fossil fuels, resulting in lower carbon dioxide emissions when burned.
- It produces about 50% less carbon dioxide emissions compared to coal and 30% less than oil.
- Additionally, the combustion of natural gas emits negligible amounts of sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter, which are major contributors to air pollution and respiratory health issues.

4. Environmental Advantages:
- The lower carbon emissions of natural gas make it a cleaner energy source in terms of greenhouse gas emissions.
- Its use in power generation can help reduce the overall carbon footprint and mitigate climate change impacts.
- Natural gas also has a lower impact on the environment during extraction and transportation compared to other fossil fuels.

5. Versatility and Applications:
- Natural gas can be used for various purposes, including electricity generation, heating, cooking, and as a fuel for vehicles.
- It is a versatile fuel that can be easily transported through pipelines, making it accessible for domestic and industrial use.

Conclusion:
Overall, natural gas is considered the cleanest fuel among the options provided due to its lower carbon content, efficient combustion process, and reduced emissions of greenhouse gases and other pollutants. Its environmental advantages, versatility, and wide range of applications make it an important energy source in the transition towards a cleaner and more sustainable energy future.