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 given ions is not colored, we need to analyze the electronic configurations of each ion and check for the presence of unpaired electrons. The presence of unpaired electrons in d-orbitals is what typically gives transition metal ions their color.

### Step-by-Step Solution:

1. **Identify the Electronic Configuration of Each Element:**
- **Manganese (Mn):** The atomic number is 25. The electronic configuration is \( [Ar] 4s^2 3d^5 \).
- **Chromium (Cr):** The atomic number is 24. The electronic configuration is \( [Ar] 4s^1 3d^5 \).
- **Zinc (Zn):** The atomic number is 30. The electronic configuration is \( [Ar] 4s^2 3d^{10} \).
- **Copper (Cu):** The atomic number is 29. The electronic configuration is \( [Ar] 4s^1 3d^{10} \).

2. **Determine the Configuration of Each Ion:**
- **Mn²⁺:** Loses 2 electrons from the 4s orbital.
- Configuration: \( 4s^0 3d^5 \) (5 unpaired electrons)
- **Cr³⁺:** Loses 3 electrons (2 from 4s and 1 from 3d).
- Configuration: \( 4s^0 3d^3 \) (3 unpaired electrons)
- **Zn²⁺:** Loses 2 electrons from the 4s orbital.
- Configuration: \( 4s^0 3d^{10} \) (0 unpaired electrons)
- **Cu²⁺:** Loses 2 electrons (1 from 4s and 1 from 3d).
- Configuration: \( 4s^0 3d^9 \) (1 unpaired electron)

3. **Analyze the Presence of 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 only ion that does not have unpaired electrons is **Zn²⁺**. Therefore, it is not colored.

### Final Answer:
The ion that is not colored is **Zn²⁺**.

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