Two isotopes of carbon are 6C12 and 6C14
The electronic configuration of 6C12 is 2, 4.
The electronic configuration of 6C14 is 2, 4.
[Isotopes have same electronic configuration]
29Ca40 and 18Ar40 are a pair of isobars
The electronic configuration of 29Ca40 is 2, 8, 8, 2
The electronic configuration of 18Ar40 is 2, 8, 8.
[Isobars have different electronic configuration]