What is radoiactivity?

Answer 1

Radioactivity is the property possessed by some elements (as uranium) or isotopes (as carbon 14) of spontaneously emitting energetic particles (as electrons or alpha particles) by the disintegration of their atomic nuclei; also : the rays emitted

Answer 2

Radioactivity is the process by which unstable atomic nuclei emit particles or energy in the form of radiation. This emission can be in the form of alpha particles, beta particles, or gamma rays. Radioactive decay results in a transformation of the original element into a different element with a more stable nucleus.