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  4. The yellow color of chromate ion and orange color of dichromate ion is due to

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Q. The yellow color of chromate ion and orange color of dichromate ion is due to

AP EAMCETAP EAMCET 2020

Solution:

In both of chromate $\left( CrO _{4}{ }^{2-}\right)$ and dichromate $\left( Cr _{2} O _{7}{ }^{2-}\right)$ ions, $Cr$ 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 $CrO _{4}{ }^{2-}$ and orange of $Cr _{2} O _{7}{ }^{2-}$ ) is the charge transfer (ligand $\rightarrow$ metal) of oxygen get transfered into vacant $d-$ orbital of $Cr ( VI)$.