The correct order of the decreasing ionic radii among the following isoelectronic species is
- Ca2+ > K+ > S2- > Cl-
- Cl- > S2- > Ca2+ > K+
- S2- > Cl- > K+ > Ca2+
- K+ > Ca2+ > Cl- > S2-
Answer
(3) S2- > Cl- > K+ > Ca2+
Solution
All four species have 18 electrons (isoelectronic).
As per NCERT, among isoelectronic species, the greater the nuclear charge, the greater the attraction for the electrons and the smaller the ionic radius.
Nuclear charge: S (16) < Cl (17) < K (19) < Ca (20)
∴ Ionic radii: S2- > Cl- > K+ > Ca2+
Answer: (3)