1. What cannot happen to energy and matter? What can happen?

The law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as the system's mass cannot change, so quantity can neither be added nor be removed.

In contrast matter can change form under different circumstances, it can also change other physical or chemical properties. Matter can take up more shape or volume mostly and has the ability to move, contract, expand, etc.