4. In which of the following ions , the colour is not due to d-d transition ? A.[Ti(H2O)6]3+ B.[CoF6]3+ C.[CrO4]2− D.[Cu(NH3)4]2+
Answer: Option C Solution: 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. For example, the orange colour of TiBr4, yellow colour of CrO42-, orange colour of Cr2O27-, intense red colour of [Fe(SCN)4] and 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.
