JEE Main · 2004 · 24 Apr 2004 · Offline · Atomic Structure

Which one the following sets of ions represents the collection of isoelectronic species?

(A) $K^{+}, Ca^{2 +}, Sc^{3 +}, Cl^{-}$ ✓ Correct
(B) $Na^{+}, Mg^{2 +}, Al^{3 +}, Cl^{-}$
(C) $K^{+}, Cl^{-}, Mg^{2 +}, Sc^{3 +}$
(D) $Na^{+}, Ca^{2 +}, Sc^{3 +}, F^{-}$

Answer: (A)

Solution

Isoelectronic species must all carry the same number of electrons. Take

K X^{+}

Ca X^{2 +}

Sc X^{3 +}

and

Cl X^{-}

: potassium drops one from nineteen to eighteen, calcium loses two from twenty to eighteen, scandium loses three from twenty-one to eighteen, and chlorine adds one onto seventeen to reach eighteen. Every member settles on the eighteen-electron argon configuration, so this is the truly isoelectronic set.

JEE Main · 2004 · 24 Apr 2004 · Offline · Single correct option

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