Atoms & structure
Isobar — আইসোবার
Quick answer
Isobars are atoms of different elements that share the same mass number but not the same proton count.
Definition
Isobars are atoms of different elements that have the same mass number: their protons plus neutrons add up to the same total, but the individual counts differ. Argon-40 (18 protons, 22 neutrons), potassium-40 (19, 21) and calcium-40 (20, 20) are the textbook trio — all A = 40, all different elements. Contrast isotopes, which share protons but differ in neutrons. In exams, one quick check settles it: same Z means isotope, same A means isobar.
For example
Argon-40 and calcium-40 both clock in at mass number 40 — one is the calm gas riding in every breath you take, the other the metal strengthening your bones.