Atoms

Binding energy per nucleon measures the stability of nucleus. In order to compare the stability of the nuclei, of different atoms, binding energy per nucleon is determined. Higher the binding energy per nucleon more stable is the nucleus. The curve has almost a flat maximum roughly from A = 50 to A = 80 corresponding to an average BE per nucleon of about 8.5 MeV. The nuclei having mass number between 50 and 80 are most stable.
Iron
having BE per nucleon of about 8.8 MeV is most stable.