Which one of the following sets of ions represents the collection of isoelectronic species?
(a) K+ , Ca2+ , Sc3+ , Cl–
(b) Na+ , Ca2+ , Sc3+ , F–
(c) K+ , Cl– , Mg2+ , Sc3+
(d) Na+ , Mg2+ , Al3+ , Cl– .
(Atomic nos.: F = 9, Cl = 17, Na = 11, Mg = 12, Al = 13, K = 19, Ca = 20, Sc = 21)