Chemistry - Mole Concept Question with Solution | TestHub

(2) ${\mathrm{Ca}}^{2+}=20-2=18{\mathrm{e}}^{-}$ $\begin{array}{rl}& \mathrm{Ar}=18{\mathrm{e}}^{-}\\ & {\mathrm{K}}^{+}=19-1=18{\mathrm{e}}^{-}\\ & {\mathrm{Cl}}^{-}=17+1=18{\mathrm{e}}^{-}\end{array}$ So, ${\mathrm{Ca}}^{2+},\mathrm{Ar},{\mathrm{K}}^{+}$and ${\mathrm{Cl}}^{-}$are isoelectronic species.