Answer the following questions related to the concept of mass defect and nuclear binding energy.
(i) Define the mass defect of a nucleus.
(ii) Explain briefly why the measured mass of a nucleus is always less than the sum of the rest masses of its free protons and neutrons.
(iii) Show that the energy corresponding to the mass defect equals the nuclear binding energy, starting from the relation between mass and energy.
(iv) The binding energy per nucleon of 56Fe is approximately 8.8MeV. Interpret this statement in physical terms.