Which of the following pairs of compounds is expected to exhibit same colour in aqueous solution ?

Options

A. `FeCI_(2),CuCI_(2)`
B. `VOCI_(2),CuCI_(2)`
C. `VOCI_(2),FeCI_(2)`
D. `FeCI_(2),MnCI_(2)`

Answer

To determine which pair of compounds exhibits the same color in aqueous solution, we need to analyze the electronic configurations and the number of unpaired electrons of the transition metal ions present in each compound. The color in transition metal complexes arises due to d-d transitions, and compounds with the same number of unpaired electrons typically exhibit the same color.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given in the question are FeCl2, CuCl2, VOCl2, and MnCl2.

2. **Determine the Oxidation States and Electronic Configurations**:
- **FeCl2**: Iron (Fe) is in the +2 oxidation state. The electronic configuration is:
- Fe: [Ar] 3d^6
- Unpaired Electrons: 4 (because the configuration can be represented as ↑↓ ↑ ↑ ↑)
- **CuCl2**: Copper (Cu) is in the +2 oxidation state. The electronic configuration is:
- Cu: [Ar] 3d^9
- Unpaired Electrons: 1 (configuration: ↑↓ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑)
- **VOCl2**: Vanadium (V) is in the +4 oxidation state. The electronic configuration is:
- V: [Ar] 3d^1
- Unpaired Electrons: 1 (configuration: ↑)
- **MnCl2**: Manganese (Mn) is in the +2 oxidation state. The electronic configuration is:
- Mn: [Ar] 3d^5
- Unpaired Electrons: 5 (configuration: ↑↓ ↑ ↑ ↑ ↑)

3. **Compare the Number of Unpaired Electrons**:
- FeCl2: 4 unpaired electrons
- CuCl2: 1 unpaired electron
- VOCl2: 1 unpaired electron
- MnCl2: 5 unpaired electrons

4. **Identify Pairs with the Same Number of Unpaired Electrons**:
- CuCl2 (1 unpaired electron) and VOCl2 (1 unpaired electron) are the only pair that has the same number of unpaired electrons.

5. **Conclusion**: Therefore, the pair of compounds that is expected to exhibit the same color in aqueous solution is **VOCl2 and CuCl2**.