`[Ti(H_(2)O)_(6)]^(3+)` is coloured while `[Sc(H_(2)O)_(6)]^(3+)` is colourless.This is because `Ti^(3+)`has one electron in the d-orbital `( 3d^(1))` which can absorb energy corresponding to yellow wavelength and undergo d-d transition (from `t_(2g)` to `e_(g))`. Bu`Sc^(3+)` is `3d^(0)`,i.e., it has no electron in 3d subshell.
