The correct answer is (c) Methane.
Methane is the main component of biogas, making up about 50-75% of the gas. It is a colorless, odorless, and flammable gas that is lighter than air. Methane is produced by the anaerobic decomposition of organic matter, such as manure, sewage, and food waste. It is also produced by the fermentation of plant material, such as rice straw and sugarcane bagasse.
Methane is a valuable fuel that can be used to generate electricity, heat homes and businesses, and power vehicles. It is also a renewable energy source that can help reduce greenhouse gas emissions.
Butane and propane are also flammable gases that are produced by the anaerobic decomposition of organic matter. However, they are not as common in biogas as methane. Ethane is a hydrocarbon that is not produced by the anaerobic decomposition of organic matter. It is a component of natural gas and is used as a fuel in some applications.
In conclusion, methane is the main component of biogas and is the most common gas used as a fuel gas.