Which element has the most stable nucleus among all naturally occurring elements?

Iron-56 is often described as having the highest binding energy per nucleon among common nuclei, which is why iron is considered exceptionally stable. This does not mean iron is “hardest” in every sense, but it is central to nuclear physics because neither fusion nor fission of iron generally releases energy easily. That stability is one reason massive stars eventually build up iron before they can no longer gain energy from fusion. Iron’s nuclear stability has profound consequences for stellar evolution.