A

In negative beta decay (β- decay), a neutron in the nucleus of an atom converts into a proton, emitting a beta particle (which is an electron) and an antineutrino.
Step 1: Understand that in β- decay, the process can be represented as:
N \rightarrow P + e^- + \bar{nu}
where N is the neutron, P is the proton, e^- is the emitted electron, and \bar{nu} is the antineutrino.
Step 2: This process increases the number of protons in the nucleus, which increases the atomic number of the atom.
Therefore, the correct answer is Option A.