The nuclear fuel in the sun is:

Why is there a need to harness non-conventional sources of energy? Give two main reasons.

List two forms of energy in which solar energy manifests itself in oceans.

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

Give two merits of solar cells.

Name the agent which decomposes animal dung into biogas. Describe the steps involved in the process.