Question

What is a radioactive isotope? Why are they radioactive?

Answer 1

Hint : In order to answer this question, to know about the radioactive isotope, we should go through the whole concept of isotope with radioactive decay and we will also discuss why they are radioactive.

Complete Step By Step Answer:
Radioactive isotope, also called radioisotope, radionuclide, or radioactive nuclide, any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays.
Every chemical element has one or more radioactive isotopes. For example, hydrogen, the lightest element, has three isotopes with mass numbers 1, 2, and 3. Only hydrogen-3 (tritium), however, is a radioactive isotope, the other two being stable. More than 1,000 radioactive isotopes of the various elements are known. Approximately 50 of these are found in nature; the rest are produced artificially as the direct products of nuclear reactions or indirectly as the radioactive descendants of these products.
Radioactive isotopes have many useful applications. In medicine, for example, $cobalt - 60$ is extensively employed as a radiation source to arrest the development of cancer. Other radioactive isotopes are used as tracers for diagnostic purposes as well as in research on metabolic processes.
The key concept is to remember that radioactive decay is a method for unstable nuclei to release energy, causing a reconfiguration of the structure of the nucleus which brings it to a lower potential energy state.

Note :
If an isotope has an unstable nucleus that breaks down to emit radiation, then these are what we call radioactive isotopes, also known as radioisotopes. Radioactive isotopes have an unstable nucleus that decays or emits excess energy or radiation until the nucleus becomes stable. They can be naturally occurring or artificial isotopes of an element.