Which part of the solar cooker is responsible for the greenhouse effect?

Ranvir lives in a village and uses wood as a fuel. He studied in his school that charcoal is a better fuel than wood. He decided to use charcoal instead of wood.
$(a)$ How can Ranvir obtain charcoal from wood?
$(b)$ Why is charcoal considered a better fuel than wood? (Give two reasons)

State whether the following statement is true or false:
Reflectors are used in solar heating devices to concentrate the sun's heat.

Give one example each for renewable and non-renewable sources of energy.

Write two different ways of harnessing energy from the ocean.

Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea in different ways?