The yellow colour of chromate ion and orange colour of dichromate ion is due to
The yellow colour of chromate ion and orange colour of dichromate ion is due to
\(d\)-d transition only
charge transfer only
both \(d-d\) transition and charge transfer
\(s-d\) transitions only
Solution
In both of chromate \(\left(\mathrm{CrO}_4^{2-}\right)\) and dichromate \(\left(\mathrm{Cr}_2 \mathrm{O}_7^{2-}\right)\) ions, \(\mathrm{Cr}\) is present in +6 oxidation state, i.e. \(d^0\)-configuration. So, \(d-d\) transition is absent in both of the ions.
Their intense colour (yellow of \(\mathrm{CrO}_4^{2-}\) and orange of \(\mathrm{Cr}_2 \mathrm{O}_7^{2-}\)) is the charge transfer (ligand \(\longrightarrow\) metal) of oxygen get transfered into vacant \(d\)-orbital of \(\mathrm{Cr}\) (VI).