The correct statement is:
After the ejection of an alpha particle, the remaining nucleus has a mass number that is four less and an atomic number that is two less, so alpha decay is not a type of nuclear fission.
In alpha decay, an alpha particle (which consists of 2 protons and 2 neutrons) is emitted from a nucleus, resulting in a decrease of the mass number by 4 and the atomic number by 2. Additionally, alpha decay is not classified as fission; it is a different type of nuclear process.