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 particle) of mass `4.0015`a.m.u. The binding energy of the helium nucleus will be `(1 a.m.u. = 931 MeV)`.
A. `28.4MeV`
B. `20.8MeV`
C. `27.1MeV`
D. `14.2MeV`