Answer the following:

Give one reason to prove that light is a form of energy.

Light which we see is basically a electromagnetic radiation, The photon is the basic "unit" of light and all forms of electromagnetic radiation are the force carrier for the electromagnetic force.
And as we know energy is the ability to do work on another physical system, also one form of energy can be converted into other. So light photon can cause electricity (which is a form of energy) and the photon possesses some energy which used in exciting electron of a conductor.
This we all have experienced when we go out in the blazing sun you feel your body getting warmed up which shows light possess energy (heat a form of energy).