Which of the following ions would form (i) coloured and (ii) colourless complexes in water?
`CU^(2+),Zn^(2+),Ti^(3+),Ti^(+4),Cd^(2+),Mn^(2+)`

Answer

(i) `Ti^(3+)(3d^(1),Cu^(2+)(3d^(9))` have unpaired electron (s). Thus they are coloured due to `d-d` transition of electrons according to `CFT`.
(ii) zn^(2+)` (3d^(10)),Ti^(+4)(3d^(0)) and Cd^(2+)(4d^(10))` do not have unpaired electron(s). Thus they do not under go d-d transition of electrons according to `CFT` and , therefore are, colourless.