Two atoms are said to be isobars if:

1.  They have the same atomic number but different mass numbers.
2.  They have the same number of electrons but a different number of neutrons.
3.  They have the same number of neutrons but different numbers of electrons.
4.  Sum of the number of protons and neutrons is the same but the number of protons is different.

 Hint: Element have same mass number and different atomic number

Isobars have the same mass number (i.e., the sum of protons and neutrons) but a different atomic number (i.e., number of protons). e.g., \(Ar_{18}^{40}\) are \(K_{19}^{40}\) isobars.

Ar1840

K1940

Atomic number=18

Atomic number=19

Mass number=40

Mass number=40