In which of the following decay processes does the element remain unchanged?

Step-by-step solution

In -decay, an excited nucleus transitions to a lower energy state by emitting a gamma-ray photon. The atomic number Z and mass number A of the nucleus remain unchanged during this process. Since the atomic number Z determines the identity of the element, the element remains unchanged. In -decay, Z decreases by 2 . In ^- -decay, Z increases by 1 . In ^+ -decay, Z decreases by 1 . Therefore, the element remains unchanged only in -decay.