(b) $\ _{1}H^{2} +_{1}H^{2} \rightarrow_{2}He^{4} +$ energy
Binding energy of a $(\ _{1}H^{2})$ deuterium nuclei
$= 2 \times 1.1 = 2.2\ MeV$
Total binding energy of two deuterium nuclei
$= 2.2 \times 2 = 4.4\ MeV$
Binding energy of a $(\ _{2}H^{4})$ nuclei $= 4 \times 7 = 28\ MeV$
So, energy released in fusion $= 28 - 4.4 = 23.6\ MeV$