Question

The following ion shows colour not due to d-d transistion.

• A. $C{r}_{2}O{{}_7}^{2-}$
• B. $MnO{{}_4}^{-}$
• C. $CrO{{}_4}^{2-}$
• D. All

Answer 1

The correct option is D All

All are coloured not due to d-d transition but due to charge transfer theory. They are coloured, though there are no unpaired electrons, because of "CHARGE TRANSFER SPECTRUM" (ie). Colour is associated with the electrons being promoted from one energy level to another, and absorbing or emitting the energy difference between the two levels. Thus transfer of an electron from M to L or viceverse results in charge transfer which gives rise to a spectra called charge transfer spectra.