Question

When a radioactive isotope releases an alpha particle, the mass number of the atom is

decreased by two.

decreased by four.

increased by two.

increased by four.

Answer 1

Alpha radiation consists of alpha particles. An alpha particle is identical to the nucleus of a helium atom, which comprises two protons and two neutrons.
When an alpha particle is emitted from a nucleus the nucleus loses two protons and two neutrons. This means the atomic mass number decreases by 4 and the atomic number decreases by 2.