The masses of neutron and proton are 1.0087 a.m.u. and 1.0073 a.m.u. respectively. If the neutrons and protons combine to form a helium nucleus (alpha particles) of mass 4.0015 a.m.u. The binding energy of the helium nucleus will be (1 a.m.u.= 931 MeV)

28.4 MeV 20.8 MeV 27.3 MeV 14.2 MeV

28.4 MeV

B.E.= $\Delta m c^2=[2(1.0087+1.0073)-4.0015]$ = 28.4 MeV