`Ti^(3+), V^(3+), Mn^(2+), Fe^(3+), Co^(2+)` form coloured aqueous solutions but `Sc^(3+), Cu^(+)` do not - explain.

Explanation

The outer electronic configurations of the given ions are as follows :
`Ti^(3+) : 3d^(1)4s^(0), Mn^(2+) : 3d^(5)4s^(0)`
`V^(3+) : 3d^(2)4s^(0), Fe^(3+) : 3d^(5)4s^(0)`
`Cu^(+) : 3d^(10)4s^(0), Co^(2+) : 3d^(7)4s^(0)`
`Sc^(3+) : 3d^(0)4s^(0)`
From the above configurations we can say that : `Ti^(3+), V^(3+), Mn^(2+), Fe^(3+)` and `Co^(2+)` ions form coloured aqueous solutions because these ions have incompletely filled d - subshell thereby allowing d - d transition to take place. `Sc^(3+)` does not have any d - electron while `Cu^(+)` has completely filled d - orbitals. Hence, these two ions do not form coloured solutions.