Name the clean fuel which can be obtained from cow-dung.

Hint: A fuel different from natural gas that can be burned to produce heat energy. It is a renewable source of energy produced biologically through anaerobic digestive rather than a fossil fuel produced by biological process. The clean fuel obtained from the cow-dung is colorless.

Complete answer:
As we know the fuel is any material that can be burned to produce heat energy. It can be a gas, coal, or oil. Biogas is a fuel produced from cow dung. It is a mixture of gases produced by knocking down organic material in the absence of oxygen. We know that methane and carbon dioxide are primary constituents of biogas. Biogas is primarily comparatives of methane gas, carbon dioxide gas and some amount of nitrogen, hydrogen and carbon monoxide.

We can say that the biogas is renewable, as well as a clean source of energy as it is produced by bio digestion. It is non-polluting and helps reduce greenhouse emission. It is also eco -friendly. Making a biogas is simple and low cost that encourages circular energy. With advantages there are some disadvantages too like fuel after refinement and compress still custom impurity. The temperature required for bacteria to digest is $37^\circ \,{\text{C}}$. It will require heat energy to maintain a biogas supply.

We know that natural gas is colorless highly flammable gaseous hydrocarbon consisting primarily of methane and ethane. It is a type of petroleum that commonly occurs in association with crude oil. A fossil fuel, natural gas is used for electricity generation, heating, and cooking and as a fuel for certain vehicles. Ethane, butane, propone, pentanes, hydrogen sulphide, carbon dioxide, water vapor, and occasionally helium and nitrogen may be present in natural gas. In order to be used for energy, methane is processed and separated from the other components.

Note: The biogas production can be costly at first since it requires construction of dome shaped structure to digest the cow dung. Once it is constructed, it will not cost us money but requires regular supply of cow dung. The use of biogas is eco-friendly and the government gives concession for the construction of biogas.