Let the mass number and atomic number of element A be M and Z, respectively. The following changes shall occur during disintegration:
MZA−α−−−−−→M−4Z−2B−β−−−−−→M−4Z−1C−β−−−−−→M−4ZD
A and D are isotopes as both have same value of Z.
B,C and D are isobars as these have same values of atomic mass.