Name the main constituent of biogas.

$(a)$ Why is the solar cooker box covered with a plane glass plate?
$(b)$ Why is energy of water flowing in a river considered to be an indirect form of solar energy?
$(c)$ How is the fission of ${}^{235}U$ nucleus brought about?

Which of the following sources of energy is different from the other?

Name the process by which energy is produced in a nuclear reactor.

Mention three advantages of converting domestic sewage to sewage gas.

Increasing demand for fossil fuels has caused harm to our environment. List its three ill-effects. Suggest three measures to reduce the consumption of fossil fuels.