When the nucleons of a nucleus are separated, a certain amount of energy is to be given to the nucleus, which is known as the binding energy.Binding energy = [(Number of nucleons)  x (Mass of a nucleon) - (Mass of the nucleus)] When the nucleons of a nucleus are separated, the increase in the total mass comes from the binding energy, which is given to the nucleus to break-off its constituent nucleons as energy is related to mass by the relation given below.E = Δmc2