The chief constituent of biogas is methane. List any two other constituents of biogas.

Compare and contrast bio-mass and hydro-electricity as sources of energy.

Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.

Solar cooker takes more time as compared to the $LPG$ to boil potato or rice,yet Kunal uses solar cooker for such type of cooking:
$(a)$ Why does Kunal use solar cooker instead of $LPG$? Give reason for your answer.
$(b)$ Name the phenomenon which is responsible for obtaining high temperature in solar cooker?
$(c)$ What is the motivation behind using solar cooker?

Compare the advantages of generating energy from biomass with those of generating it from a hydropower plant.

$(a)$ Classify the two fuels, $CNG$ and hydrogen, as renewable and non-renewable.
$(b)$ Justify the statement, "Hydrogen is a cleaner and better fuel than $CNG$."