${}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{X}$,${}_{{\mathrm{Z}}_1}{}^{{\mathrm{A}}_1}\mathrm{Y}$and ${}_{19}{}^{40}\mathrm{K}$ are isobars.Identify correct statement from the following?

Nuclides having same mass number but different atomic numbers are called as isobars

${}_{18}{}^{40}\mathrm{Ar},{}_{19}{}^{40}\mathrm{K} \mathrm{and} {}_{20}{}^{40}\mathrm{Ca}$ are isobars