Final answer:
An atom with the appropriate n/p ratio is stable and resides within the band of stability. Atoms in this band have a balanced proportion of neutrons to protons, with heavier stable nuclei having more neutrons than protons. Atoms outside this band are radioactive.
Step-by-step explanation:
When an atom has the appropriate neutron-to-proton (n/p) ratio, it is generally considered stable and will fall within the band of stability. Atoms that are located in the middle of the band of stability have a balanced n/p ratio that adheres to the principles that dictate nuclear stability. Lighter stable nuclei generally have an n/p ratio of 1:1, while heavier stable nuclei have a slightly higher proportion of neutrons to protons.
For example, nitrogen-14, a lighter nuclide, has an equal number of protons and neutrons, while lead-207, a heavier nuclide, has 125 neutrons to 82 protons, making its n/p ratio 1.52. Atoms outside this band exhibit radioactivity, spontaneously decaying over time to achieve a more favorable n/p ratio that brings them closer to, or into, the band of stability.