Which sequence is an example of radioactive decay?

An example of a radioactive decay would be a polonium isotope becoming a lead isotope when the polonium nuclide emits two protons and two neutrons. A radioactive decay is a process that involves an atom that has an unstable nucleus losing energy through emitting radiation in the form of alpha, gamma or beta particles. This process happens because there is unstability since all materials would want to be stable. This process is used in dating materials in order to know the age of thes materials. It is based on the amount of a radioactive isotope that is naturally occurring left on the material and the decay products that is involved.