10), the number of protons and
the number of neutrons are the same on the two sides of the equation (b) We know that the binding energy of a nucleus gives a negative
contribution to the mass of the nucleus (mass defect) Now, since
proton number and neutron number are conserved in a nuclear
reaction, the total rest mass of neutrons and protons is the same
on either side of a reaction But the total binding energy of nuclei
on the left side need not be the same as that on the right hand
side