<Dl> <Dd> This is a list of the chemical elements and their isotopes, listed in terms of stability . </Dd> </Dl> <Dd> This is a list of the chemical elements and their isotopes, listed in terms of stability . </Dd> <P> Atomic nuclei consist of protons and neutrons, which attract each other through the nuclear force, while protons repel each other via the electric force due to their positive charge . These two forces compete, leading to some combinations of neutrons and protons being more stable than others . Neutrons stabilize the nucleus, because they attract protons, which helps offset the electrical repulsion between protons . As a result, as the number of protons increases, an increasing ratio of neutrons to protons is needed to form a stable nucleus; if too many or too few neutrons are present with regard to the optimum ratio, the nucleus becomes unstable and subject to certain types of nuclear decay . Unstable isotopes decay through various radioactive decay pathways, most commonly alpha decay, beta decay, or electron capture . Many other rare types of decay, such as spontaneous fission or cluster decay are known . (See radioactive decay for details .) </P>

Which of the nuclides below would be the most stable fe-56 he-3 ba-139 c-12