Question

Which one of the following ion exhibits d-d transition and paramagnetism as well?

• A. $MnO_{4}^{-}$
• B. $Cr_{2}O_{7}^{2 -}$
• C. $CrO_{4}^{2 -}$
• D. $MnO_{4}^{2 -}$

Answer 1

Answer: (D)

As d-d transition and paramagnetism is possible in presence of unpaired $e^{-}$ , so here $MnO_{4}^{2 -}$ shows it.

$CrO_{4}^{2 -}\Rightarrow Cr^{6 +}=\left[\right.Ar\left]\right.$

Unpaired electron (n) = 0; Diamagnetic

$Cr_{2}O_{7}^{2 -}\Rightarrow Cr^{6 +}=\left[\right.Ar\left]\right.$

Unpaired electron (n) = 0; Diamagnetic

$MnO_{4}^{2 -}=Mn^{6 +}=\left[\right.Ar\left]\right.3d^{1}$

Unpaired electron (n) = 1; Paramagnetic

$MnO_{4}^{-}=Mn^{7 +}=\left[\right.Ar\left]\right.3d^{0}$

Unpaired electron (n) = 0; Diamagnetic