The atom with the highest nuclear binding energy is generally considered to be iron-56 (56Fe). Nuclear binding energy is the energy required to completely separate the nucleus of an atom into its individual protons and neutrons. It is a measure of the stability of the nucleus.
Iron-56 has the highest nuclear binding energy per nucleon (proton or neutron) among all naturally occurring elements. This means that, on average, the binding of nucleons within the iron-56 nucleus is the strongest, making it the most stable nucleus in terms of binding energy. This stability arises from a balance between the attractive nuclear force and the repulsive electromagnetic force between protons.
Iron-56 is abundant in the cores of massive stars and plays a crucial role in stellar nucleosynthesis. It is often referred to as the "most stable" or "most tightly bound" nucleus because it has the highest average binding energy per nucleon. However, it's important to note that there are other isotopes, particularly within the transuranic elements, that can have higher binding energies per nucleon when they are synthesized in laboratories, but they are highly unstable and not naturally occurring.