What is a solar panel?

$A$ student constructed a box-type solar cooker. He found that it is not working efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the solar cooker. What maximum temperature can ordinarily be reached inside a solar cooker?

Mention two disadvantages of using animal dung directly as a fuel.

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)

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?

Write the composition and source of $LPG$. Although liquefied gas is present in the cylinder,how does it appear as a gas in the burner?