Which one of the following species will impart colour to an aqueous solution?

Step-by-step solution

The colour of transition metal ions in aqueous solution is due to d-d transitions, which require the presence of unpaired d-electrons (partially filled d-subshell). The electronic configurations of the given ions are: Cr ³⁺ (Z = 24): [ Ar ] 3d^3 (3 unpaired electrons) Cu ^+ (Z = 29): [ Ar ] 3d¹⁰ (0 unpaired electrons) Zn ²⁺ (Z = 30): [ Ar ] 3d¹⁰ (0 unpaired electrons) Ti ⁴⁺ (Z = 22): [ Ar ] 3d^0 (0 unpaired electrons) Since Cr ³⁺ has a partially filled d-subshell, it will undergo d-d transitions and impart colour t