Question

Which of the following is not an isoelectronic species?

• A. $C{l}^{-},P^{3-},Ar$
• B. $N^{3-},Ne,M{g}^2$
• C. $B^3,He,Li$
• D. $N^{3-},S^{2-},C{l}^{-}$

Answer 1

The correct option is D

$N^{3-},S^{2-},C{l}^{-}$

Isoelectronic species are the species which have the same number of electrons.
Let's check out number of electrons in each option.

$C{l}^{-}\to 17+1=18electrons$

$P^{3-}\to 15+3=18electrons$

$Ar\to 18electrons$

Yes

$N^3{N}^3\to 7+3=10electrons$

$Ne\to 10electrons$

$M{g}^{+2}\to 12-2=10electrons$

Yes

$B{B}^{+3}\to 5-3=2electrons$

$He\to 2electrons$

$L{i}^{+}\to 3-1=2electrons$

Yes

$S^2\to 16+2=18electrons$

$N^{3-}{N}^{3-}\to 7+3=10electrons$

$S^2{S}^2\to 16+2=18electrons$

$MgM{g}^{+2}\to 17+1=18electrons$