The two processes are as follows: ZAX⟶Z−2A−4Y+24He Z−2A−4Y⟶A−4ZZ+ee− Since X and Z have same atomic number, that is, same number of protons but different atomic mass, that is, sum of number of protons and neutrons. We know isotopes are atoms with same number of protons but different number of neutrons. Therefore, X and Z are isotopes.