Q. In which of the following ions, the colour is not due to d-d transition?
Answer: MnO(–)4
Notes: The colour of transition-metal compounds is normally associated with d-d transitions. However, some transition metal compounds show intense colour in solution in spite of absence of d-electrons. The deep purple of MnO4 are not due to d-d transitions. In the case of MnO4 ion, the color is due to charge transfer and not due to d-d transitions.