Which of the following is not coloured

Options

A. `Mn^(2+)`
B. `Cr^(3+)`
C. `Zn^(2+)`
D. `Cu^(2+)`

Answer

To determine which of the following transition metal ions is not colored, we need to analyze the electron configurations of each ion and check for the presence of unpaired electrons. Transition metals exhibit color due to d-d transitions, which occur when unpaired electrons absorb energy and move to a higher energy level. The color observed is complementary to the color of light absorbed.

### Step-by-Step Solution:

1. **Identify the Transition Metal Ions**:
We need to consider the transition metal ions provided in the question. Let's assume the options are Mn²⁺, Cr³⁺, Zn²⁺, and Cu²⁺.

2. **Determine the Electron Configuration**:
- **Mn²⁺**:
- Atomic number of Mn = 25.
- Electron configuration of Mn: [Ar] 4s² 3d⁵.
- For Mn²⁺, we remove 2 electrons from the 4s orbital:
- Configuration: [Ar] 3d⁵ (5 unpaired electrons).
- **Cr³⁺**:
- Atomic number of Cr = 24.
- Electron configuration of Cr: [Ar] 4s² 3d⁵.
- For Cr³⁺, we remove 3 electrons (2 from 4s and 1 from 3d):
- Configuration: [Ar] 3d³ (3 unpaired electrons).
- **Zn²⁺**:
- Atomic number of Zn = 30.
- Electron configuration of Zn: [Ar] 4s² 3d¹⁰.
- For Zn²⁺, we remove 2 electrons from the 4s orbital:
- Configuration: [Ar] 3d¹⁰ (0 unpaired electrons).
- **Cu²⁺**:
- Atomic number of Cu = 29.
- Electron configuration of Cu: [Ar] 4s² 3d¹⁰.
- For Cu²⁺, we remove 2 electrons (1 from 4s and 1 from 3d):
- Configuration: [Ar] 3d⁹ (1 unpaired electron).

3. **Analyze Unpaired Electrons**:
- Mn²⁺: 5 unpaired electrons → colored.
- Cr³⁺: 3 unpaired electrons → colored.
- Zn²⁺: 0 unpaired electrons → **not colored**.
- Cu²⁺: 1 unpaired electron → colored.

4. **Conclusion**:
The transition metal ion that is not colored is **Zn²⁺** because it has no unpaired electrons.

### Final Answer:
**Zn²⁺ is not colored.**

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