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

Only those ions will be coloured which have incomplete d-orbitals, Ions which has complete or complete d-orbitals are colourless.
`{:(Ti^(3+) = [Ar]3d^(1),"Purple"),(V^(3+) = [Ar]3d^(2),"Green"),(Cu^(+) = [Ar]3d^(10),"Colourless"),(Sc^(3+) = [Ar],"Colourless"),(Mn^(3+) = [Ar]3d^5,"Pink"),(Fe^(3+) = [Ar] 3d^6,"Brown"),(Co^(2+) = (Ar) 3d^7,"Pink"):}`
As `Sc^(3+)` and `Cu^(+)` have `3d^(0) and 3d^(10)` configuration in their valence shell so their aqueous solution are colourless. All other i.e., `Ti^(3+), V^(3+), Mn^(2+), Fe^(3+) and Co^(2+)` are coloured in aqueous medium.