Question

Which of the following is iso-electronic?

• A. ${CN}^{-},CO$
• B. $N{O}_2,C{O}_2$
• C. ${N{O}_2}^{-},C{O}_2$
• D. $S{O}_2,C{O}_2$

Answer 1

The correct option is A

${CN}^{-},CO$

Now,

What do you mean by iso-electronic?

Iso-electronic $⟹$ which have same number of electrons

So, lets calculate the number of electrons in each one of them.

(a) $C{N}^{-}\Rightarrow$ (C = 6 electrons and N = 7 electrons) + 1 electrons (Because of negative charge) = 14 electrons

$CO\Rightarrow$ (C = 6 electrons and O = 8 electrons) = 14 electrons

(b) $C{O}_2\Rightarrow$ (C = 6 electrons and $O_2=8$ $\times$ 2 = 16 electrons) = 22 electrons

$N{O}_2\Rightarrow$ (N = 7 electrons and $O_2=8$ $\times 2=16$ electrons) = 23 electrons

(c) ${N{O}_2}^{-}\Rightarrow$ (23 electrons + 1 electrons) (Because of negative Charge) = 24 electrons

$C{O}_2\Rightarrow$ (C = 6 electrons and $O_2=8$ $\times$ 2 = 16 electrons) = 22 electrons

(d) $S{O}_2\Rightarrow$ (S = 16 electrons and $O_2$ = 16 electrons) = 32 electrons

$C{O}_2\Rightarrow$ (C = 6 electrons and $O_2$ = 16 electrons ) = 22 electrons

Therefore, we can see that in only option (a), the number of electrons is same for both the molecules.