Question

What is nuclear energy?

Answer 1

The energy released during nuclear fission or fusion,especially when used to generate electricity .

Answer 2

The energy released during nuclear fission (separating a nucleus of atom to form other atom) or fusion(adding mass to  a nucleus of atom),especially when used to generate electricity .
nuclear energy is commonly generated by fusion..
it is performed more using hydrogen .../
hydrogen's nuclei's mass is 1 ...it is converted by adding more mass to its nuclei to form a helium atom