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^2_1\\\\) +\\\\(H^2_1\\\\)→ \\\\(H^3_2 \\\\)+ \\\\(n^2_1\\\\) + \\\\(energy\\\\)