When a radioactive isotope releases an alpha particle, the atomic number of the atom is (2 points) decreased by one. increased by one. decreased by two. increased by four.

When alpha decay takes place, two protons and two neutrons are forcefully ejected from the nucleus in a way that looks very similar to a Helium nucleus. This type of decay causes the atomic mass of the parent particle to drop by four (four particles lost), but the atomic number drops by only two (two protons lost). Therefore, your answer is C.