Answer
Isotopes are elements that have the same number of protons, but different numbers of neutrons. Non-radioactive elements are elements that do not spontaneously decay, meaning that they do not emit radiation. Therefore, all isotopes of non-radioactive elements are non-radioactive. For example, carbon-12 and carbon-13 are both isotopes of carbon, but carbon-12 is stable, while carbon-13 is radioactive.