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

1. ${\mathrm{MnO}}_4^{-}$
2. ${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}$
3. ${\mathrm{CrO}}_4^{2-}$
4. ${\mathrm{MnO}}_4^{2-}$

Solution

$\begin{array}{ccc}{\mathrm{CrO}}_4^{-2}& {\mathrm{Cr}}^{+6}& \mathrm{diamagnetic}\end{array}$
$\begin{array}{ccc}{\mathrm{Cr}}_2{\mathrm{O}}_7^{-2}& {\mathrm{Cr}}^{+6}& \mathrm{diamagnetic}\end{array}$
$\begin{array}{ccc}{\mathrm{MnO}}_4^{-}& {\mathrm{Mn}}^{+7}& \mathrm{diamagnetic}\end{array}$
$\begin{array}{ccc}{\mathrm{MnO}}_4^{-2}& {\mathrm{Mn}}^{+6}& \mathrm{Paramagnetic}\end{array}$   
Unpaired electron is present so d-d transition is possible.

Asked in: NEET 2018

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