Question

What exactly makes a substance radioactive?

Answer 1

An atom is radioactive if it is unstable. A nucleus is said to be unstable if the ratio of neutrons to protons (n/p) in the nucleus of an atom does not lie in the range 1-1.5. If the n/p ratio is more or less than this value (that is one of the particles of the nucleus is too less or too more), then the forces of attraction and repulsion between the nucleons are not in balance, thus resulting in radioactivity.