Which of the following group does not represent the isoelectronic species?

Atoms and ions with the same number of electrons are referred to as isoelectronic species. Or, an isoelectronic pair is a pair of species with the same amount of electrons that combines all the atoms of a given species. The radii of isoelectronic species might vary due to various nuclear charges.

Here,

The no of electron for ${\mathrm{H}}_2\mathrm{S},{\mathrm{K}}^{+},\mathrm{Ar},\mathrm{Cl}$ are 18,18,18 and 17 respectively.

So, ${\mathrm{H}}_2\mathrm{S},{\mathrm{K}}^{+},\mathrm{Ar},\mathrm{Cl}$ does not represent the isoelectronic species.

Hence, Option D is correct.