Question

Which one of the following groups represents a collection of isoelectronic species?
(At. nos.: Cs-55, Br-35)

• A. $N{a}^{+}$, $C{a}^{2+}$, $M{g}^{2+}$
• B. $N^{3-}$, $F^{-}$, $N{a}^{+}$
• C. $Be$, $A{l}^{3+}$, $C{l}^{-}$
• D. $C{a}^{2+}$, $C{s}^{+}$, $Br$

Answer 1

Answer: (B)

$N^{3-},F^{-},N{a}^{+}$ represents a collection of iso-electronic species. They have 10 electrons each. Iso-electronic species have the same number of electrons.
The atomic numbers of $N,F$ and $Na$ are 7,9 and 11 respectively.
Number of electrons in $N^{3-}=7+3=10$.
Number of electrons in $F^{-}=9+1=10$.
Number of electrons in $N{a}^{+}=11-1=10$.