Question

Which of the following pairs has both the ions coloured in aqueous solution? [Atomic numbers of Sc = 21, Ti = 22, Ni = 28, Cu = 29, Mn = 25]

• A. Sc³⁺, Mn²⁺
• B. Ni²⁺, Ti⁴⁺
• C. Ti³⁺, Cu⁺
• D. Mn²⁺, Ti³⁺

Answer 1

The Correct Option is D

The colours of ions in aqueous solution depend on the presence of unpaired electrons in the d-orbitals of the metal ion, which can absorb specific wavelengths of light. The following points apply:

• Sc³⁺ has no d-electrons, so it is colourless in aqueous solution.
• Mn²⁺ has a d⁵ configuration and is coloured (it absorbs visible light).
• Ni²⁺ and Ti⁴⁺ are both colourless in aqueous solution (Ni²⁺ has a d⁸ configuration, and Ti⁴⁺ has no d-electrons).
• Cu⁺ is colourless, as it has a d¹⁰ configuration (full d-orbital).
• Ti³⁺ has a d¹ configuration and is coloured in aqueous solution.

Thus, the correct pair where both ions are coloured in aqueous solution is Mn²⁺ and Ti³⁺.

The correct answer is (D) : Mn²⁺, Ti³⁺.