Question

If both the number of protons and the number of neutrons are conserved in each nuclear reaction in what way is mass converted into energy (or vice-versa) in a nuclear reaction?

Answer 1

The sum of masses of nuclei of product element is less than sum of masses of reactants and hence, loss of mass takes place during the reaction. This difference of mass of product element and reactant converts into energy and liberated in the form of heat.

$H_1^2$ +$H_1^2$→ $H_2^3$+ $n_1^2$ + $energy$