A student sketches the qualitative curve of average binding energy per nucleon Ebn versus mass number A and observes that it rises steeply for light nuclei, reaches a maximum near A≈56, and then falls gradually for heavier nuclei.
(i) Describe two physical reasons that account for the initial rapid rise of Ebn with increasing A for light elements.
(ii) Explain why the curve attains a broad maximum in the region A≈50–60.
(iii) State how the shape of this curve explains why nuclear fusion of very light nuclei and nuclear fission of very heavy nuclei are both energy-releasing processes.