(Mass defect and nuclear binding concepts)
(i) Define mass defect and nuclear binding energy of a nuclide.
(ii) Explain, with the help of mass–energy equivalence, why the mass of a bound nucleus is less than the sum of the masses of its constituent free nucleons although no nucleon is destroyed.
(iii) Describe qualitatively how the variation of binding energy per nucleon with mass number leads to energy release in both nuclear fission of heavy nuclei and fusion of light nuclei.