Which of the following complex ions is expected to absorb visible light?

Options

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

Explanation

To determine which of the following complex ions is expected to absorb visible light, we need to analyze the electronic configurations and the presence of unpaired electrons in the given complexes. The absorption of visible light occurs when electrons transition from a lower energy level to a higher energy level, which is facilitated by the presence of unpaired electrons.

### Step-by-Step Solution:

1. **Identify the Complexes**: We need to analyze the given complexes. For this example, let's assume we have the following complexes:
- A) Sc(H2O)3
- B) Cr(NH3)6^3+
- C) CoCl4^2-
- D) Ni(CN)4^2-

2. **Calculate the Oxidation State**:
- For **A) Sc(H2O)3**:
- Scandium (Sc) is in the +3 oxidation state.
- The electronic configuration of Sc is [Ar] 4s² 3d¹.
- In the +3 state, it loses 2 electrons from 4s and 1 from 3d, resulting in [Ar] (no unpaired electrons).
- For **B) Cr(NH3)6^3+**:
- Chromium (Cr) is also in the +3 oxidation state.
- The electronic configuration of Cr is [Ar] 4s¹ 3d⁵.
- In the +3 state, it loses 1 electron from 4s and 2 from 3d, resulting in [Ar] 3d³ (3 unpaired electrons).
- For **C) CoCl4^2-**:
- Cobalt (Co) is in the +2 oxidation state.
- The electronic configuration of Co is [Ar] 4s² 3d⁷.
- In the +2 state, it loses 2 electrons from 4s and 1 from 3d, resulting in [Ar] 3d⁶ (4 unpaired electrons).
- For **D) Ni(CN)4^2-**:
- Nickel (Ni) is in the +2 oxidation state.
- The electronic configuration of Ni is [Ar] 4s² 3d⁸.
- In the +2 state, it loses 2 electrons from 4s and remains with 3d⁸ (2 unpaired electrons).

3. **Determine Magnetic Properties**:
- **A) Sc(H2O)3**: Diamagnetic (no unpaired electrons).
- **B) Cr(NH3)6^3+**: Paramagnetic (3 unpaired electrons).
- **C) CoCl4^2-**: Paramagnetic (4 unpaired electrons).
- **D) Ni(CN)4^2-**: Paramagnetic (2 unpaired electrons).

4. **Conclusion**: The complexes that can absorb visible light must have unpaired electrons. Therefore, the complexes that can absorb visible light are:
- **B) Cr(NH3)6^3+**
- **C) CoCl4^2-**
- **D) Ni(CN)4^2-**

Among these, **B) Cr(NH3)6^3+** is a common example of a complex that absorbs visible light due to its unpaired electrons.

### Final Answer:
The complex ion expected to absorb visible light is **B) Cr(NH3)6^3+**.