(b) Mention any three applications of radioactive isotopes.

Radioactive isotopes:

1. The isotopes whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiations in the form of alpha, beta, and gamma rays are known as radioactive isotopes.
2. All chemical element has one or more radioactive isotopes.
3. Examples of radioactive isotopes: Carbon$-14$, Uranium$-235$, Sodium$-24$, Iodine$-131$, etc.

Applications of radioactive isotopes:

1. Radioactive isotopes in medicine: Iodine$-131$ is effective in locating brain tumors and in determining liver and thyroid activity.
2. Radioactive isotopes in nuclear power plants: Uranium$-235$ is used as a fuel in nuclear reactors of nuclear power plants for generating electricity.
3. Radioactive isotope in industries: Tritium, a radioactive isotope of hydrogen, is used to identify the leaks in underground water pipes.