Question 15

Identify the central metal ion: $Mn^{3+}$ has electronic configuration $[Ar] 3d^4$.

For $[\text{Mn(Br)}_6]^{3-}$: $Br^-$ is a weak field ligand (WFL). The configuration is $t_{2g}^3 e_g^1$. Number of unpaired electrons ($n$) $= 4$. $\mu_1 = \sqrt{n(n+2)} = \sqrt{4(4+2)} = \sqrt{24} \approx 4.899\text{ B.M.}$

For $[\text{Mn(CN)}_6]^{3-}$: $CN^-$ is a strong field ligand (SFL). The configuration is $t_{2g}^4 e_g^0$. Number of unpaired electrons ($n$) $= 2$. $\mu_2 = \sqrt{2(2+2)} = \sqrt{8} \approx 2.828\text{ B.M.}$

Total sum $= 4.899 + 2.828 = 7.727\text{ B.M.}$