Which one among the following complex ions has the highest paramegnetism?

Options

A. `[Cr(H_(2)O)_(6)]^(3+)`
B. `[Fe(H_(2)O)_(6)]^(2+)`
C. `[Cu(H_(2)O)_(6)]^(2+)`
D. `[Zn(H_(2)O)_(6)]^(2+)`

Answer

To determine which complex ion has the highest paramagnetism, we need to identify the number of unpaired electrons in each of the given complex ions. The complex with the highest number of unpaired electrons will exhibit the highest paramagnetism.

### Step-by-Step Solution:

1. **Identify the oxidation states and electronic configurations of the metal ions:**
- **Chromium (Cr³⁺):**
- Atomic number = 24
- Electronic configuration of Cr = [Ar] 4s² 3d⁴
- For Cr³⁺, we remove 3 electrons: [Ar] 3d³
- **Iron (Fe²⁺):**
- Atomic number = 26
- Electronic configuration of Fe = [Ar] 4s² 3d⁶
- For Fe²⁺, we remove 2 electrons: [Ar] 3d⁶
- **Copper (Cu²⁺):**
- Atomic number = 29
- Electronic configuration of Cu = [Ar] 4s² 3d¹⁰
- For Cu²⁺, we remove 2 electrons: [Ar] 3d⁹
- **Zinc (Zn²⁺):**
- Atomic number = 30
- Electronic configuration of Zn = [Ar] 4s² 3d¹⁰
- For Zn²⁺, we remove 2 electrons: [Ar] 3d¹⁰

2. **Determine the number of unpaired electrons:**
- **Cr³⁺ (3d³):**
- Configuration: ↑ ↑ ↑ (3 unpaired electrons)
- **Fe²⁺ (3d⁶):**
- With H₂O as a weak field ligand, it will be high spin:
- Configuration: ↑ ↑ ↑ ↑ (4 unpaired electrons)
- **Cu²⁺ (3d⁹):**
- Configuration: ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ (1 unpaired electron)
- **Zn²⁺ (3d¹⁰):**
- Configuration: ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ (0 unpaired electrons)

3. **Compare the number of unpaired electrons:**
- Cr³⁺: 3 unpaired electrons
- Fe²⁺: 4 unpaired electrons
- Cu²⁺: 1 unpaired electron
- Zn²⁺: 0 unpaired electrons

4. **Conclusion:**
- The complex ion with the highest number of unpaired electrons is **Fe²⁺** with **4 unpaired electrons**. Therefore, it exhibits the highest paramagnetism.

### Final Answer:
The complex ion with the highest paramagnetism is **Fe²⁺**.