The correct option is C ligand to metal charge transfer
The purple colour of KMnO4 ion is due to ligand to metal charge transfer.
In KMnO4, the central manganese atom has +7 oxidation state. As we know, Manganese has the atomic number of 25 and since the charge is +7, the number of total electrons will be 18. The electronic configuration can be written as [Ar]3d04s0. Here, also there are no unpaired electrons and hence d-d transition can't occur.
The oxygen in KMnO4 will donate electrons to the vacant orbitals of manganese and as a result a charge transfer spectra occurs and therefore we can say that the colour of KMnO4 also arises from charge transfer spectra.