Which of the following ions will exhibit colour in aqueous solutions ?

Step-by-step solution

Key Idea:- Colour is obtained as a consequence of d-d( or f-f) transition, and for d-d (or f-f) transition, presence of unpaired electrons is the necessary condition. gathered La ³⁺( Z =57)=[ Xe ] 4 f ^0 5 ~d ^0 6 ~s ^0 (no unpaired electron) Ti ³⁺( Z =22)=[ Ar ] 3 ~d ^1 4 ~s ^0 (one unpaired electron) Lu ³⁺( Z =71)=[ Xe ] 4 f ¹⁴ 5 ~d ^0 6 ~s ^0 (no unpaired electron) Sc ³⁺( Z =21)=[ Ar ] 3 ~d ^0 4 ~s ^0 gathered (no unpaired electron) Hence, only Ti ³⁺ will exhibit colour in aqueous solution.