Which of the following complexions is expected to absorb visible light ? (Al. No. Zn=30, SC=21, Ti= 22, Cr= 24)

Options

A. `[Ti(en)_(2)(NH_(3))_(2)]^(4-)`
B. `[Cr(NH_(3))_(6)]^(3+)`
C. `[Zn(NH_(3))_(6)]^(2+)`
D. `[Sc(H_(2)O)_(3)(NH_(3))_93)]^(3+)`

Answer

To determine which of the given complex ions is expected to absorb visible light, we need to analyze the electronic configurations of the metal ions in the complexes and their oxidation states. The ability to absorb visible light is associated with d-d transitions, which occur when there are unpaired electrons in the d-orbitals of the metal ion.

### Step-by-Step Solution:

1. **Identify the Metal Ions and Their Oxidation States:**
- **Zinc (Zn)**: Atomic number 30. In the complex, Zn is typically in the +2 oxidation state.
- **Scandium (Sc)**: Atomic number 21. In the complex, Sc is in the +3 oxidation state.
- **Titanium (Ti)**: Atomic number 22. In the complex, Ti is in the +4 oxidation state.
- **Chromium (Cr)**: Atomic number 24. In the complex, Cr is in the +3 oxidation state.

2. **Determine the Electron Configurations:**
- **Zinc (Zn²⁺)**: The electron configuration is [Ar] 3d¹⁰. Since all d-orbitals are filled, there are no unpaired electrons, and it cannot absorb visible light.
- **Scandium (Sc³⁺)**: The electron configuration is [Ar] 3d². There are 2 unpaired electrons, which allows for d-d transitions and the absorption of visible light.
- **Titanium (Ti⁴⁺)**: The electron configuration is [Ar] 3d⁰. There are no d-electrons, so it cannot absorb visible light.
- **Chromium (Cr³⁺)**: The electron configuration is [Ar] 3d³. There are 3 unpaired electrons, which allows for d-d transitions and the absorption of visible light.

3. **Conclusion:**
- The complexes that can absorb visible light are those with unpaired d-electrons.
- **Scandium (Sc³⁺)** and **Chromium (Cr³⁺)** can absorb visible light due to their unpaired electrons.
- Among the options, **Chromium (Cr³⁺)** is the most notable because it is known for its vibrant colors in complexes.

### Final Answer:
**Chromium (Cr³⁺)** is expected to absorb visible light.