A stable atom is one that does what?

• A. Doesn't change
• B. Changes often
• C. Radioactive
• D. Has no neutrons

Answer: (A)

Stability means the nucleus does not undergo spontaneous decay. A stable atom keeps its number of protons and neutrons and doesn’t emit radiation that would change it into something else. Because of that, the atom stays the same over time—the nucleus isn’t changing, even if electrons might rearrange in chemical reactions. The other ideas describe unstable atoms: changing often would imply decay, and being radioactive is just another way of saying the atom decays. Having no neutrons isn’t a defining feature of stability, since many stable atoms do have neutrons (and some light stable isotopes have none, like hydrogen-1).