From the graph, it is clear that it has a peak near $A=60$. Nuclei around this are most stable. (Example : Iron) The shape of this curve suggests two possibilities for converting significant amounts of mass into energy : (i) Fission Reactions From the curve, the heaviest nuclei are less stable than the nuclei near $A=60$. This suggests that energy can be released if heavy nuclei split apart into smaller nuclei. This process is called fission. (ii) Fusion Reactions The curve also suggests energy can be released from the lighter elements (like hydrogen and helium) have nuclei those are less stable than heavier elements up to $A \sim 60$. Thus, sticking two light nuclei together to form a heavier nucleus can also release energy. This process is called fusion. In both fission and fusion reactions, the total masses after the reaction are less than those before. This "missing mass" appears as energy.