Question

Among `[TiF_(6)]^(2-),[COF_(6)]^(3-),CU_(2)Cl_(2)` and `[NiCl_(4)]^(2-)["Atomic number",Ti=22,Co=27,Cu=29,Ni=28]` the Colourless species are:
A. `[TiF_(6)]^(2-)` and `[Cu_(2)Cl_(2)]`
B. `[Cu_(2)Cl_(2)]` and `[NiCl_(4)]^(2-)`
C. `[TiF_(6)]^(3-)` and `[CoF_(6)]^(3-)`
D. `[CoF_(6)]^(3-)` and `[NiCl_(4)]^(2-)`

Answer 1

Correct Answer - A
In `[TiF_(6)]^(2-)` the titanium is +4 oxidation state having the electronic configuration `[Ar]^(18)3d^(0)4S^(0)`. Similarly in `Cu_(2)Cl_(2)` the copper is in `+1` oxidation state having the electronic configuration ` [Ar]^(18)3d^(0)4S^(0)`. As they do not have any unpaired electrons for d-d transition, they are therefore colourless.In `[NiCl_(4)]^(2-)` the nickel is in `+2` oxidation state and electronic configuration is `[Ar]^(18)3d^(8)4S^(0)` . As it has two unpaired electrons, so the complex is coloured.
In `[CoF_(6)]^(3-)`. the cobalt is in `+3` oxidation state having electron configuration ` [Ar]3d^(6)4S^(0)`. As it has four unpaired electron , so the complex is coloured.