Question

Which one of the following has lowest value of paramagnetic behaviour?

• A. $\left[Cr\right(CN{)}_6{]}^{3-}$
• B. $\left[Mn\right(CN{)}_6{]}^{3-}$
• C. $\left[Fe\right(CN{)}_6{]}^{3-}$
• D. $\left[Co\right(CN{)}_6{]}^{3-}$

Answer 1

Answer: (D)

$\left[Co\right(CN{)}_6{]}^{3-}$

Cental metal atom in the compound having less number of unpaired electrons has the lowest value of paramagnetic behavior.

(1) $C{r}^{3+}\to 3d^{3}4s^0$ no. of unpaired $e^{-}=3$

(2) $M{n}^{3+}\to 3d^{4}4s^0$ no. of unpaired $e^{-}=2$

(3) $F{e}^{3+}\to 3d^{5}4s^0$ no. of unpaired $e^{-}=1$

(4) $C{o}^{3+}\to 3d^{6}4s^0$ no. of unpaired $e^{-}=0$

So, $Co$ in $\left[Co\right(CN{)}_6{]}^{3-}$ is having the least number of unpaired electrons i.e. $0$. So, it is a diamagnetic compound that means less paramagnetic comparatively.

Hence option D is correct.