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

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

$(a)$ How does the construction of dams across rivers get linked with the production of greenhouse gases?
$(b)$ How do technological inputs improve the efficiency of biomass fuels?

Biomass has been used as fuel since ancient times. How has it been modified to function as a more efficient fuel in the recent past?

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?

Aditya suggests his family to install a solar water heater at their residence. But some of the family members were in favour of installing an electric geyser.
$(a)$ Who,according to you,is taking a correct decision? Mention the value exhibited by Aditya.
$(b)$ Also,give reasons (at least $2$) for your answer.