Binding energy curve (average binding energy per nucleon in MeV against number of nucleons in nucleus) for a number of relatively common (abundant) isotopes (not chosen systematically; almost anything with an occurence of over .2 was chosen though a few exceptions are in there, such as U235). A few important ones for the purposes of nuclear fusion and nuclear fission are marked, as well as iron-56, which sits at the highest point on this graph and cannot yield energy from fusion or fission.
<ul><li><a href="//commons.wikimedia.org/wiki/File:Binding_energy_curve_-_common_isotopes.svg" title="File:Binding energy curve - common isotopes.svg">Binding energy curve - common isotopes.svg</a>: <a href="//commons.wikimedia.org/w/index.php?title=User:Fastfission&amp;action=edit&amp;redlink=1" class="new" title="User:Fastfission (page does not exist)">Fastfission</a></li>
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<a href="//commons.wikimedia.org/wiki/File:Binding_energy_curve_-_common_isotopes.svg" title="File:Binding energy curve - common isotopes.svg">Binding energy curve - common isotopes.svg</a>