Name any two materials that are used to make solar cells.

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 is the basic cause for winds to blow? Name a part of India where wind energy is commercially harnessed. Compare wind power and power of water flow in respect of generating mechanical and electrical energies. What is the hindrance in developing them?

Why is a biogas plant a safe and efficient method of waste disposal? Justify.

"$A$ biogas plant solves the fuel as well as environmental problems". Discuss.

Mention any two advantages and two disadvantages of producing hydroelectricity by building dams on rivers.