What exactly is radioactivity?

Q8. What exactly is radioactivity?

Ans.  THE ATOMS OF AN ELEMENT MAY COME IN SEVERAL DIFFERENT FORMS OR ISOTOPES.   

Each form has a different number of neutrons in the nucleus, indicated in the name, as in carbon-12 and carbon-14. The nuclei of some of these isotopes- the ones scientific call radioisotopes- are unstable, and they decay (break up), releasing radiation, consisting of streams of particles called alpha, beta and gamma rays. This is what radioactivity is.