Question

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

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Answer 1

$Cr{O}_4^{2-}\text{Electronic configuration}C{r}^{6+}=\left[Ar\right]$
Unpaired electron (n) = 0; hence diamagnetic.
Hence, there is no d-d transition and no paramagnetism.

$C{r}_2{O}_7^{2-}\text{Electronic configuration}C{r}^{6+}=\left[Ar\right]$
Unpaired electron (n) =0; hence diamagnetic.
Hence, there is no d-d transition and no paramagnetism. Its colour is due to charge transfer spectra.

$Mn{O}_4^{2-}\text{Electronic configuration}M{n}^{6+}=\left[Ar\right]3d^1$
Unpaired elctron (n) = 1; hence paramagnetic
Unpaired elctron gives rise to d-d transition and paramagnetism.

$Mn{O}_4^{-}\text{Electronic configuration}M{n}^{7+}=\left[Ar\right]$
Unpaired electron (n) =0; hence diamagnetic
Hence, there is no d-d transition and no paramagnetism. Its colour is due to charge transfer spectra.

Option (c) is correct