Which elements are used to make a solar cell?

The energy liberated by burning $1 \,g$ of charcoal is approximately: (in $,kJ$)

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

Why are biogas plants considered to be a boon to farmers? Give reasons.

What are the drawbacks of using nuclear energy?

State whether the following statement is true or false:
Solar energy has the greatest potential of all the renewable sources of energy.