The type of radioactive decay in which the atomic number of the product increases by one is known as beta decay. Beta decay involves the emission of a beta particle, which can be either an electron (β-) or a positron (β+).
In β- decay, a neutron in the nucleus of an atom is converted into a proton, and an electron is emitted. The atomic number increases by one because the number of protons in the nucleus increases by one. The mass number remains the same since the number of protons and neutrons collectively remains constant.
In β+ decay, a proton in the nucleus is converted into a neutron, and a positron is emitted. The atomic number decreases by one because the number of protons in the nucleus decreases by one. Again, the mass number remains unchanged.
Both β- and β+ decay involve changes in the atomic number while keeping the mass number relatively constant, resulting in the formation of a different element or isotope.