Question

What is the name given to element with same mass number and different atomic number?

Answer 1

1. The element having the same mass number but a different atomic number is called isobars.
2. For example ${}_{18}{}^{40}\mathrm{Ar},{}_{19}{}^{40}\mathrm{K}$and ${}_{20}{}^{40}\mathrm{Ca}$
3. Here mass number of all three elements are $40$ but the atomic number is different.

Hence, the name given to an element with the same mass number and different atomic number is isobar.