Which of the following ions is colourless in solution?

Options

A. `V^(3+)`
B. `Cr^(3+)`
C. `Co^(2+)`
D. `Sc^(3+)`

Answer

D

Explanation

`V(23=[Ar]3d^(3),4s^(2)`
`V^(3+)=[Ar]3d^(2),4s^(0)` (Two unpaired electrons)
`Cr(24)=[Ar]3d^(5),4s^(1)`
`Cr^(3+)=[Ar]3d^(3+),4s^(0)` (Three unpaired electrons)
`Co(27)=[Ar]3d^(7),4s^(2)`
`Co^(2+)=[Ar]3d^(7),4s^(0)` (Three unpaired electrons)
`Sc(21)=[Ar]3d^(1),4s^(2)`
`Sc^(3+)=[Ar]3d^(0),4s^(0)` (No unpaired electrons)
Thus, in `Sc^(3+)` no unpaired d-electrons is present. Hence, no d-d transition is possible and it is colourless ion .