Chemistry - Mole Concept Question with Solution | TestHub

Isobars are atoms of different elements having the same mass number but different atomic numbers.

In the pair ${}^{40}{\text{K}}_{19}$ and ${}^{40}{\text{Ca}}_{20}$, both have the same mass number $40$ but different atomic numbers $19$ and $20$ respectively.

Thus, they represent a pair of isobars.

Answer: ${}^{40}{\text{K}}_{19}$ and ${}^{40}{\text{Ca}}_{20}$