When the nucleus increases its charge by one after emitting a particle, it means this particle is beta, specificallt, an electron called a negative beta particle. Basically, a beta particle forms when a netruon changes to a proton and a high-energy electron, the proton stays in the nuclues, and the electron is released as beta radiation. When this situation occurs, the mas number stays the same, the atomic number increases by 1, and the nuclear charge increases by 1.
Therefore, the answer is a negative beta particle.