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

Draw the diagram of the floating gas holder type biogas plant and mark on it the gas outlet.

Which gas is present both in natural gas and biogas?

Vinod is a member of the school Eco-club. He knows about a school that is a zero-garbage zone. He expressed his willingness to his teachers to implement the same in his school. He decided to place different coloured dustbins for segregating biodegradable and non-biodegradable garbage as the first step. Now answer the following questions.
$(a)$ Why does Vinod want to segregate biodegradable and non-biodegradable waste?
$(b)$ What can Vinod do with the biodegradable waste?

What do you suggest to overcome the problem of "limitation of sources of energy"? Mention any three suggestions for the effective use of energy.

What do you mean by 'ocean thermal energy'? How can electricity be generated from this energy?