A nucleus of mass number A splits symmetrically into two fragments each of mass number A/2. If the binding energy per nucleon of the parent nucleus is b1 and that of each fragment is b2:
(i) Derive an expression for the total energy released ΔE in terms of A, b1 and b2.
(ii) State the condition on b1 and b2 for the process to be exothermic.