Question

The complex ion which has no $d$-electron in the central metal atom is :

• A. ${\left[Mn{O}_4\right]}^{-}$
• B. ${\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}$
• C. ${\left[Fe{\left(CN\right)}_6\right]}^{3-}$
• D. ${\left[Cr{\left(H_{2}O\right)}_6\right]}^{3+}$

Answer 1

Answer: (A)

${\left[Mn{O}_4\right]}^{-}$

Electronic configuration of manganese is $\left[Ar\right]3d^{5}4s^2$

In $Mn{O}_4^{-}$, manganese is in $M{n}^{+7}$.

Electronic configuration of manganese $M{n}^{+7}$ $\left[Ar\right]3d^{0}4s^0$

Electronic configuration of cobalt is $\left[Ar\right]3d^{7}4s^2$

Cobalt is in $C{o}^{+3}$

Electronic configuration of $C{o}^{+7}$ $\left[Ar\right]3d^{6}4s^0$

Electronic configuration of iron is $\left[Ar\right]3d^{6}4s^2$

Iron is in $F{e}^{+3}$

Electronic configuration of $F{e}^{+3}$ $\left[Ar\right]3d^{5}4s^0$

Electronic configuration of chromium is $\left[Ar\right]3d^{5}4s^1$

Cobalt is in $C{r}^{+3}$

Electronic configuration of $C{r}^{+3}$ $\left[Ar\right]3d^{3}4s^0$

Hence, option $A$ is correct.