Question

multiple choice question
what is an ion?
an atom with an unstable nucleus
an atom with too many or too few neutrons
an atom that has gained or lost electrons
an atom that emits radiation

Explanation:

An ion is formed when an atom gains or loses electrons, resulting in a charged particle. An atom with an unstable nucleus is a radioactive atom. An atom with too many or too few neutrons may be unstable but not necessarily an ion. An atom that emits radiation is a radioactive atom.

Answer:

An atom that has gained or lost electrons