Radioactive decay occurs when atoms
a) lose mass.
b) join with atoms of another element.
c) break down to form atoms of another element.
d) are exposed to chemical weathering.

for your !

C) break down to form atoms of another element.

Explanation:

The process of radioactive decay, synonymous for half-life (t1 / 2) or half-disintegration period (P), is the statistical phenomenon that allows us to predict how long a given number of atoms will produce radioactive emissions. This statistical forecast assumes the transmutation (decay synonym) of 50% of radioactive atoms in a given period of time. Since the process is continuous, there is a radioactive decay curve that tends infinitely to zero.