Isobars are the elements that contain similar nucleon count (sum of the protons and neutrons). The series of elements having 40 Mass numbers serve as good examples; 4017Cl, 4016S, 4019K, 4020Ca, and 4018Ar. The nucleus of all the elements, which are given here, contains a similar number of particles present in the nucleus, but they contain a differential number of protons and neutrons.