Why are solar cookers covered with a glass plate?

The longest and the shortest wavelengths (in $\mu m$) for red and violet light are respectively:

"Electricity generated by the water stored in a dam can be considered to be another form of solar energy." Explain by describing the series of energy transformations in sequence taking place during the process.

Why is $CNG$ considered an environmentally friendly fuel?

Why is there a need to harness non-conventional sources of energy? Give two main reasons.

Why are biogas plants considered to be a boon to farmers? Give reasons.