Question

Maximum value of paramagnetism is shown by

• A. $ \left[Fe \left(CN\right)_{6}\right]^{3-} $
• B. $ \left[Cr \left(CN\right)_{6}\right]^{3-} $
• C. $ \left[Co \left(CN\right)_{6}\right]^{3-} $
• D. $ \left[Sc \left(CN\right)_{6}\right]^{3-} $

Answer 1

Answer: (B)

Paramagnetism is shown due to unpaired electrons. Since, $CN^-$ is a strong field ligand, it causes pairing of electrons.
$(a)$ In $[Fe(CN)_6]^{3-}, Fe^{3+} = Ar[3d^5]$

$1$ unpaired electron
$(b)$ In $[Cr(CN)_6]^{3-}, Cr^{3+} =Ar[3d^3]$

$3$ unpaired electrons.
$(c)$ In $[Co(CN)_6]^{3-}, Co^{3+} = Ar[3d^6]$

No unpaired electron.
$(d)$ In $[Sc (CN)_6]^3, Sc^{3+} = Ar[3d]^{\circ}$

No unpaired electron.
Hence, $[Cr(CN)_6]^{3-}$ will show maximum paramagnetism.