Chemistry - Mole Concept Question with Solution | TestHub

Key Idea Iso electronic species are those which have same number of electrons. The total number of electrons in the given species are as follows $\begin{array}{rl}{\mathrm{H}}_2\mathrm{S}& =2+16=18\text{ electrons }\\ {\mathrm{F}}_2& =9+9=18\text{ electrons }\\ {\mathrm{O}}^{2-}& =8+2=10\text{ electrons }\\ {\mathrm{Ca}}^{2+}& =20-2=18\text{ electrons }\\ {\mathrm{Sc}}^{3+}& =21-3=18\text{ electrons }\end{array}$ Thus, ${\mathrm{O}}^{2-}$ (oxide ion) is not iso electronic with ${\mathrm{H}}_2\mathrm{S}$.