Question

which best describes a radioactive isotope?
o an atom is unstable.
o an atom is stable.
o there is only one other isotope.
o there are many isotopes.

Explanation:

A radioactive isotope has an unstable nucleus which undergoes radioactive decay to become more stable. Stability of an atom is related to the balance of protons and neutrons in the nucleus. Unstable atoms are radioactive.

Answer:

An atom is unstable.