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

Explanation

Ions having incompletely filled d - subshell are likely to be coloured due to possibility of d-d transition by absorbing visible light. Those with completely filled or empty d - orbitals are colourless. Thus `Ti^(3+)(d^(1)), V^(3+)(d^(2)), Mn^(2+)(d^(5)), Fe^(3+)(d^(5)), Co^(2+)(d^(7))` are coloured due to d - d transition. `Cu^(+)(d^(10))` and `Sc^(3+)(d^(0))` are colourless.