List two non-conventional sources of energy.

State two merits of hydroelectricity.

$A$ modern selenium solar cell can convert $25 \%$ of sunlight into electrical energy.

The chief constituent of biogas is methane. List any two other constituents of biogas.

$(a)$ $A$ hydropower plant converts one form of energy into another. Name these two forms of energy.
$(b)$ State two advantages of generating hydroelectricity compared to the generation of electricity in a thermal power plant.

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)