Explain the processes of nuclear fission and nuclear fusion by using the plot of binding energy per nucleon (BE/A) versus the mass number A.

Nuclear Fission:

When a heavy nucleus (A > 235 say) breaks into two lighter nuclei (nuclear fission), the binding energy per nucleon increases i.e, nucleons get more tightly bound. This implies that energy would be released in nuclear fission.

Nuclear Fusion:

When two very light nuclei join to form a heavy nucleus, the binding is energy per nucleon of fused heavier nucleus more than the binding energy per nucleon of lighter nuclei, so again energy would be released in nuclear fusion.

Example:${}_{1}H^2 + {}_{1}H^2 \underset{ }{\to } {}_{2}H{e}^4 + 26 Mev$

BE Graph: