Predict which of the following will be coloured in aqueous solution? `Ti^(3+),V^(3+),Cu^(o+),Sc^(3+),Mn^(2+),Fe^(2+)` and `Co^(2+)` Give reasons for each.

Explanation

Only the ions that have electrons in d-orbital and in which d-d transition is possible will be coloured. The ions in which d-orbitals are empty or completely filled will be colourless as no d-d transition is possible in those configurations.
From the above table, it can be easily observed that only `Sc^(3+)` has an empty d-orbital and `Cu^(+)` has completely filled d-orbitals. All other ions, except `Sc^(3+)` and `Cu^(+)`, will be coloured in aqueous solution because of d−d transitions.