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

To solve this problem, we need to evaluate the color of different metal ions in aqueous solutions, which depends on their electronic configuration and the nature of their d-orbitals.

1. Electronic Configurations and Oxidation States:
The color of a metal ion in solution is often due to d-d transitions in the case of transition metal ions. For the following ions, we need to determine if both are colored in aqueous solutions:

- Scandium (Sc): The electronic configuration of Sc is [Ar] 3d¹ 4s². In its +3 oxidation state, Sc has the configuration [Ar], which means it has no d-electrons and does not show color in aqueous solution.

- Titanium (Ti): The electronic configuration of Ti is [Ar] 3d² 4s². In its +3 oxidation state, Ti has the configuration [Ar] 3d¹, which makes it colored in aqueous solution due to d-d transitions.

- Nickel (Ni): The electronic configuration of Ni is [Ar] 3d⁸ 4s². In its +2 oxidation state, Ni has the configuration [Ar] 3d⁸, and the Ni²⁺ ion is colored due to the presence of d-electrons.

- Copper (Cu): The electronic configuration of Cu is [Ar] 3d¹⁰ 4s¹. In its +2 oxidation state, Cu has the configuration [Ar] 3d⁹, and Cu²⁺ is colored in aqueous solution due to d-d transitions.

- Manganese (Mn): The electronic configuration of Mn is [Ar] 3d⁵ 4s². In its +2 oxidation state, Mn has the configuration [Ar] 3d⁵, and Mn²⁺ is not strongly colored because the d-orbital is fully occupied in a stable arrangement. However, Mn³⁺ is colored in aqueous solution due to d-d transitions.

2. Analyzing the Options:
- Option (A) "Sc³⁺, Mn²⁺": Sc³⁺ is colorless as it has no d-electrons, and Mn²⁺ is also colorless because its 3d orbitals are filled. Thus, this option is incorrect. 
- Option (B) "Ni²⁺, Ti⁴⁺": Ni²⁺ is colored, but Ti⁴⁺ has an empty 3d orbital, so it does not display color. Thus, this option is incorrect. 
- Option (C) "Ti³⁺, Cu⁺": Ti³⁺ is colored, but Cu⁺ is colorless since it has a fully filled d-orbital. Thus, this option is incorrect. 
- Option (D) "Mn²⁺, Ti³⁺": Both Mn²⁺ and Ti³⁺ are colored due to d-d transitions. Thus, this option is correct.

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

Answer 2

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⁺.