From Einstein's mass energy relation ΔE=(Δm)c2
Mass of proton =1.6725×10−27kg
Mass of electron =0.0009×10−27kg
Their sum =1.6734×10−27kg
Mass of neutron =1.6747×10−27kg
Their difference Δm=0.0013×10−27kg ∴ΔE=(0.0013×10−27)(3×108)2 =1.17×10−13J
Also, 1.6×10−19J=1eV ∴ΔE=1.6×10−191.17×10−13 =0.731×106eV =0.731MeV.