Question

What is a radioactive isotope?

Answer 1

Isotopes that can emit radioactive radiations(i.e.alpha, beta and gamma rays) are called radioactive isotopes.

Explanation:

Isotopes are atoms of same elements having same atomic number but different mass number(number of protons and neutrons in nucleus).
Isotopes of elements having atomic number 82 or more are unstable and emit certain radiations. The process is called radioactivity and such isotopes are called radioactive isotopes.