Which of the following ions would form (i) coloured and (ii) colourless complexes in water?
`CU^(2+),Zn^(2+),Ti^(3+),Ti^(+4),Cd^(2+),Mn^(2+)`

Answer

To determine which ions would form colored and colorless complexes in water, we need to analyze the electronic configurations of the given ions and check for the presence of unpaired electrons. The presence of unpaired electrons in the d-orbitals is what typically leads to the formation of colored complexes due to d-d transitions.

Let's analyze each ion step-by-step:

1. **Cu²⁺ (Copper(II) ion)**:
- Electronic Configuration: The electronic configuration of Cu is [Ar] 3d¹⁰ 4s¹. When it loses two electrons to form Cu²⁺, the configuration becomes [Ar] 3d⁹.
- Unpaired Electrons: Cu²⁺ has 1 unpaired electron in the 3d subshell.
- Conclusion: Cu²⁺ will form colored complexes (specifically, blue).

2. **Zn²⁺ (Zinc(II) ion)**:
- Electronic Configuration: The electronic configuration of Zn is [Ar] 3d¹⁰ 4s². When it loses two electrons to form Zn²⁺, the configuration becomes [Ar] 3d¹⁰.
- Unpaired Electrons: Zn²⁺ has no unpaired electrons.
- Conclusion: Zn²⁺ will form colorless complexes.

3. **Ti³⁺ (Titanium(III) ion)**:
- Electronic Configuration: The electronic configuration of Ti is [Ar] 3d² 4s². When it loses three electrons to form Ti³⁺, the configuration becomes [Ar] 3d¹.
- Unpaired Electrons: Ti³⁺ has 1 unpaired electron.
- Conclusion: Ti³⁺ will form colored complexes (specifically, violet).

4. **Ti⁴⁺ (Titanium(IV) ion)**:
- Electronic Configuration: When Ti loses four electrons to form Ti⁴⁺, the configuration becomes [Ar] 3d⁰.
- Unpaired Electrons: Ti⁴⁺ has no unpaired electrons.
- Conclusion: Ti⁴⁺ will form colorless complexes.

5. **Cd²⁺ (Cadmium(II) ion)**:
- Electronic Configuration: The electronic configuration of Cd is [Kr] 4d¹⁰ 5s². When it loses two electrons to form Cd²⁺, the configuration becomes [Kr] 4d¹⁰.
- Unpaired Electrons: Cd²⁺ has no unpaired electrons.
- Conclusion: Cd²⁺ will form colorless complexes.

6. **Mn²⁺ (Manganese(II) ion)**:
- Electronic Configuration: The electronic configuration of Mn is [Ar] 3d⁵ 4s². When it loses two electrons to form Mn²⁺, the configuration becomes [Ar] 3d⁵.
- Unpaired Electrons: Mn²⁺ has 5 unpaired electrons.
- Conclusion: Mn²⁺ will form colored complexes (specifically, light pink).

### Summary:
- **Colored Complexes**: Cu²⁺, Ti³⁺, Mn²⁺
- **Colorless Complexes**: Zn²⁺, Ti⁴⁺, Cd²⁺