Answer the following questions related to mass–energy equivalence in nuclear reactions.
(i) Define the term mass defect of a nucleus.
(ii) Using the principle of conservation of mass–energy, explain why the total rest mass of the products in a nuclear reaction can differ from that of the reactants.
(iii) A student asserts that in every exothermic nuclear reaction the total rest mass of the products is always less than that of the reactants. State whether this assertion is correct and justify your answer briefly on the basis of mass–energy conservation.