Option 1: Coke - Coke is not considered a clean fuel. It is a solid fuel derived from coal and is known to release harmful emissions when burned, contributing to air pollution.

Option 2: Propane - This is the correct answer. Propane is a clean fuel. It is a hydrocarbon gas that is commonly used for heating and cooking. When burned, it produces lower emissions compared to other fossil fuels such as coal or natural gas. Propane is considered cleaner because it produces fewer greenhouse gases and particulate matter, resulting in reduced air pollution.

Option 3: Petrol - Petrol, also known as gasoline, is not considered a clean fuel. It is a fossil fuel derived from crude oil and burning petrol releases high levels of carbon dioxide (CO2) and other harmful pollutants, contributing to air pollution and climate change.

Option 4: Wax - Wax is not considered a clean fuel. It is a solid fuel derived from petroleum or plant-based sources. Burning wax releases emissions such as CO2 and volatile organic compounds (VOCs), which contribute to air pollution.

In summary, option 2 (Propane) is an example of a clean fuel due to its lower emissions and reduced air pollution compared to other fossil fuels.