Which one of the following sets of ions represents a collection of isoelectronic species? (Atomic nos.: F = 9, Cl = 17, Na = 11, Mg = 12, Al = 13, K = 19, Ca = 20, Sc = 21) - PrepBharat

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

a) K⁺, Ca²⁺, Sc³⁺, Cl^–
b) Na⁺, Ca²⁺, Sc³⁺, F^–
c) K⁺, Cl^–, Mg²⁺, Sc³⁺
d) Na⁺, Mg²⁺, Al³⁺, Cl^–

Answer: a
Explanation: Isoelectronic species are those which have same number of electrons. K⁺ = 19 – 1 = 18; Ca²⁺ = 20 – 2 = 18; Sc³⁺ = 21 – 3 = 18; Cl^– = 17 + 1 = 18. Thus all these ions have 18 electrons in them.

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