Which of the following monoatomic species have a strictly larger ionic radius than the potassium ion — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

All these species ($S^{2-}, Cl^-, K^+, Ca^{2+}, Sc^{3+}$) are isoelectronic with $18$ electrons. For isoelectronic species, the radius decreases as atomic number ($Z$) increases. Their atomic numbers are $16, 17, 19, 20, 21$ respectively. Thus, the radius order is $S^{2-} > Cl^- > K^+ > Ca^{2+} > Sc^{3+}$. Only $S^{2-}$ and $Cl^-$ are larger than $K^+$.