The metal ion which does not form coloured compound is

Options

A. Chromium
B. Zine
C. Manganese
D. Iron

Explanation

To solve the question of which metal ion does not form colored compounds, we will follow these steps:

### Step 1: Understand the Concept of Color in Metal Ions
Metal ions exhibit color in their compounds due to the presence of unpaired electrons in their d-orbitals. The presence of unpaired electrons allows for d-d transitions when light is absorbed, which results in color.

### Step 2: Identify the Metal Ions
The question likely provides a list of metal ions. For this solution, let's consider the common transition metals: Chromium (Cr), Zinc (Zn), Manganese (Mn), and Iron (Fe).

### Step 3: Write the Electronic Configurations
We need to write the electronic configurations for each of the metal ions to determine the number of unpaired electrons.

1. **Chromium (Cr)**:
- Electronic Configuration: \( \text{[Ar]} 3d^5 4s^1 \)
- Unpaired Electrons: 6 (5 from 3d and 1 from 4s)

2. **Zinc (Zn)**:
- Electronic Configuration: \( \text{[Ar]} 3d^{10} 4s^2 \)
- Unpaired Electrons: 0 (both 3d and 4s are fully filled)

3. **Manganese (Mn)**:
- Electronic Configuration: \( \text{[Ar]} 3d^5 4s^2 \)
- Unpaired Electrons: 5 (5 from 3d, 4s is fully filled)

4. **Iron (Fe)**:
- Electronic Configuration: \( \text{[Ar]} 3d^6 4s^2 \)
- Unpaired Electrons: 4 (6 from 3d, 4s is fully filled)

### Step 4: Count the Unpaired Electrons
Now, we summarize the number of unpaired electrons for each metal ion:
- Chromium (Cr): 6 unpaired electrons
- Zinc (Zn): 0 unpaired electrons
- Manganese (Mn): 5 unpaired electrons
- Iron (Fe): 4 unpaired electrons

### Step 5: Determine Which Metal Ion Does Not Form Colored Compounds
From the above analysis, we see that Zinc (Zn) is the only metal ion with 0 unpaired electrons. Therefore, Zinc does not form colored compounds.

### Final Answer
The metal ion which does not form colored compounds is **Zinc (Zn)**.

---