Question

Which of the following is not isoelectronic?

• A. $S^{2-}$
• B. $N{a}^{+}$
• C. $C{a}^{2+}$
• D. $C{l}^{-}$

Answer 1

The correct option is B $N{a}^{+}$

Among the given species, $S^{2-},C{a}^{2+},C{l}^{-}$ all are isoelectronic with 18 electrons while $N{a}^{+}$ has only 10 $e^{-}$.