The following transition metal ions would be coloured in aqueous solution except________?

The correct answer is Sc³⁺. Transition metal ions are often colored because their electrons can absorb light energy and jump to higher energy levels. When the electrons drop back down to their original energy levels, they release the energy as visible light, which we see as color. The color of the complex depends on the arrangement of the ligands around the metal ion. Scandium (Sc) has only one electron in its outermost shell, which it loses to form the Sc³⁺ ion. Since it has an empty d-orbital, it cannot absorb light in the visible region, and therefore it is colorless in aqueous solution. On the other hand, Cr³⁺, Fe³⁺, and Mn³⁺ ions have partially filled d-orbitals, which allow them to absorb light in the visible region and give them characteristic colors in aqueous solution. Cr³⁺ is violet, Fe³⁺ is yellow, and Mn³⁺ is pink.