Which statement correctly describes radioactive isotopes?

• A. They do not undergo any changes over time.
• B. They have different chemical properties compared to stable isotopes of the same element.
• C. They have unstable nuclei that spontaneously emit radiation.
• D. They have the same number of neutrons as stable isotopes of the same element.

Answer: (C)

Verified step by step guidance

1. Understand that isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
2. Recognize that radioactive isotopes, also called radioisotopes, have unstable nuclei that undergo spontaneous changes to reach stability.
3. Know that this instability causes the nucleus to emit radiation in the form of alpha, beta, or gamma particles, a process called radioactive decay.
4. Note that radioactive isotopes do not differ significantly in chemical properties from stable isotopes because chemical behavior depends mainly on the number of protons and electrons, which remain the same.
5. Conclude that the defining characteristic of radioactive isotopes is their unstable nuclei that spontaneously emit radiation, distinguishing them from stable isotopes.