Question

Which of the following are iso-electronic and iso-structural?

$N{O}_3^{-}$, $C{O}_3^{2-}$, $Cl{O}_3^{-}$, $S{O}_3$

• A. NO${}_3$${}^{-}$, CO${}_3$${}^{2-}$
• B. NO${}_3$${}^{-}$, SO${}_3$
• C. CO${}_3$${}^{2-}$, ClO${}_3$${}^{-}$
• D. CO${}_3$${}^{2-}$, SO${}_3$

Answer 1

The correct option is A

NO${}_3$${}^{-}$, CO${}_3$${}^{2-}$

The number of electrons in the following are:

$N{O}_3^{-}$ $\Rightarrow$ 7 + 8(3) + 1 = 32 electrons

$C{O}_3^{2-}$ $\Rightarrow$ 6 + 8(3) + 2 = 32 electrons

$Cl{O}_3^{-}$ $\Rightarrow$ 17 + 8(3) + 2 = 42 electrons

$S{O}_3$ $\Rightarrow$ 16 + 8(3) = 40 electrons

Now, from VSEPR, we have know the structure of $C{O}_3^{2-}$ and $N{O}_3^{-}$.

ep of $C{O}_3^{2-}$ = $\frac{V+L+A-C}{2}$ = $\frac{4+2}{2}$ = 3 $\Rightarrow$ Trigonal Planar

ep of $N{O}_3^{-}$ = $\frac{V+L+A-C}{2}$ = $\frac{5+1}{2}$ = 3 $\Rightarrow$ Trigonal Planar

ep of $S{O}_3$ =$\frac{6}{2}$ = 3 $\Rightarrow$ Trigonal Planar

ep of $Cl{O}_3^{-}$ = $\frac{7+1}{2}$ = 4 $\Rightarrow$ Tetrahedral

Therefore, ${C{O}_3}^{2-}and{N{O}_3}^{-}$ are isoelectronic and isostructural.