NEET 2023 Phase 2 · ChemistryAtomic radiusPrevious Year Question

Which one of the following represents all isoelectronic species?

Answer: (B) $Ca X^{2 +}$ , $Ar$ , $K X^{+}$ , $Cl X^{-}$ . \textbf{Answer:} (B) $Ca X^{2 +}$ , $Ar$ , $K X^{+}$ , $Cl X^{-}$ \textbf{Solution:} Isoelectronic species have the same number of electrons.

A. $Na X^{+}$ , $Mg X^{2 +}$ , $O X^{-}$ , $F X^{-}$
B. $Ca X^{2 +}$ , $Ar$ , $K X^{+}$ , $Cl X^{-}$ ✓
C. $Na X^{+}$ , $Cl X^{-}$ , $O X^{-}$ , $NO X^{+}$
D. $N X_{2} O$ , $N X_{2} O X_{4}$ , $NO X^{+}$ , $NO$

Correct Answer

(B) $Ca X^{2 +}$ , $Ar$ , $K X^{+}$ , $Cl X^{-}$

Solution & Explanation

\textbf{Answer:} (B) $Ca X^{2 +}$ , $Ar$ , $K X^{+}$ , $Cl X^{-}$ \textbf{Solution:} Isoelectronic species have the same number of electrons. In option B, $Ca X^{2 +}$ ( $18$ ), $Ar$ ( $18$ ), $K X^{+}$ ( $18$ ) and $Cl X^{-}$ ( $18$ ) all have $18$ electrons. In option A, $O X^{-}$ has $9$ electrons while $Na X^{+}$ , $Mg X^{2 +}$ and $F X^{-}$ have $10$ each, so they are not all isoelectronic. Hence B is correct.

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