When a radioactive particle is released, what is conserved in the case of alpha decay?

In the context of alpha decay, the process involves the release of an alpha particle, which consists of 2 protons and 2 neutrons (essentially a helium nucleus). During this decay, two important quantities are conserved: the atomic number and the mass number of the atom.

The atomic number, which indicates the number of protons in the nucleus, decreases by 2 because the alpha particle carries away 2 protons. Therefore, the parent nucleus transforms into a new element that has an atomic number reduced by 2. The mass number, which is the total number of protons and neutrons in the nucleus, also decreases by 4 because the alpha particle removes 2 protons and 2 neutrons from the original nucleus.

Though energy is released during this decay, the key conservation principles at play specifically relate to the atomic structure changes — the changes in atomic number and mass number due to the alpha particle's release. Thus, the correct answer reflects the specific conservation of atomic mass and the atomic number in the context of this nuclear transformation.