The increasing order of the ionic radii of the given isoelectronic species is?

(1) K+, S2-, Ca2+, Cl–

(2) Cl–, Ca2+, K+,S2-

(3) S2-, Cl–, Ca2+, K+

(4) Ca2+, K+, Cl–, S2-

Answer ::

If the atom or molecule is negatively charged, as an additional electron occupies an outer orbital, there is increased electron-electron repulsion and cause increased shielding, which pushes the electrons further apart. Since the electrons now outnumber the protons in the ion, the protons cannot pull the extra electrons as tightly toward the nucleus which results in decreased Zeff. Hence, the ionic radii increase whereas it is vice versa when it is positively charged. The increasing order of the ionic radii of the given isoelectronic species is Ca2+, K+, Cl–, S2-.