Explain why `TiCl_3` is coloured but `TiCl_4` is colourless ?

Explanation

`Ti` has electrónic configuration : `[Ar]^(18) 3d^2 4s^2`

With one electron in 3d-Subshell in `Ti^(3+)`, d-d transitions are possible and hence it is coloured with electron 3d-subshell

In `Ti^(4+)`, d-d transitions are not possible and hence it is colourless.