answer and explanation
Radioactivity is the emission of ionizing radiation from nuclear decay. there are three types of radioactive decay.
alpha decay
in alpha decay an alpha particle is released. In the parent atom, the atomic number decreases by 2 and the atomic mass decreases by 4
beta decay
in beta decay a beta particle is released, the atomic number is unchanged and the atomic mass increases by 1
gamma decay
in gamma decay, energy is released as gamma rays from an excited nuclear state. the atomic mass and atomic number remain unchanged.