Question

why KMnO4 is coloured ????​

Answer 1

The oxidation state of Mn in KMnO4 is +7, which means that Mn does not have any d electrons left. Theoretically, Mn7+ complexes should not be colored because electronic transitions are not possible (since there are no d electrons left). However, KMnO4 has a deep purple color because of charge transfer from the ligand (O2–) to the metal center. This is called a ligand-to-metal charhmge transfer. Charge transfers are beyond Laporte and spin selection rules thus they are always allowed giving the complex very high molar extinction coefficients

Answer 2

Potassium permanganate(KMnO4) is colored because it absorbs light in the visible range of the electromagnetic spectrum. The permanganate ion is the source of the color, as a ligand-to-metal charge transfer takes place between the oxygen's p orbitals and the empty d-orbitals on the metal. This charge transfer takes place when a photon of light is absorbed, which leads to the purple color of the compound.