What is the correct decreasing order of ionic radii for the given isoelectronic species? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

For an isoelectronic series (all have 18 electrons), ionic radius is inversely proportional to the nuclear charge ($Z$). Hence, the size decreases as proton count increases: $S(16) > Cl(17) > K(19) > Ca(20)$.