The spin only magnetic moments of the complexes $\left[\mathrm{Mn}(\mathrm{CN})_6\right]^{3-}$ and $\left[\mathrm{Co}\left(\mathrm{C}_2 \mathrm{O}_4\right)_3\right]^{3-}$ are respectively

• Correct answer
  A

  2.84 BM, 0 BM
• B

  0 BM, 2.84 BM
• C

  0 BM, 3.87 BM
• D

  $5.92 \mathrm{BM}, 2.84 \mathrm{BM}$

Solution

In $\left[\mathrm{Mn}(\mathrm{CN})_6\right]^{3-}$, oxidation state of Mn is $+3 \mathrm{Mn}^{3+}: \mathrm{d}^4$
Unpaired electron $=2$ $\begin{aligned} & \mu_{\text {spin only }}=\sqrt{\mathrm{n}(\mathrm{n}+2)} \mathrm{BM} \\ & =\sqrt{2(2+2)} \mathrm{BM} \\ & =2.84 \mathrm{BM} \end{aligned}$ In $\left[\mathrm{Co}\left(\mathrm{C}_2 \mathrm{O}_4\right)_3\right]^{3-}$, oxidation state of co is +3 $\mathrm{Co}^{3+}: \mathrm{d}^6$
$\begin{aligned} & \mathrm{n}=0 \\ & \mathrm{M}_{\text {spin only }}=0 \mathrm{BM}\end{aligned}$

Hence, the correct answer is option: 'A'.