Which of the following has the maximum number of unpaired d-electron?

Options

A. `Zn^(2+)`
B. `Fe^(2+)`
C. `Ni^(2+)`
D. `Cu^(2+)`

Explanation

To determine which of the given ions has the maximum number of unpaired d-electrons, we will analyze the electronic configurations of each ion step by step.

### Step 1: Identify the electronic configurations of the neutral atoms
1. **Zinc (Zn)**: Atomic number = 30
- Electronic configuration: \[ \text{Zn: } [\text{Ar}] 3d^{10} 4s^2 \]

2. **Iron (Fe)**: Atomic number = 26
- Electronic configuration: \[ \text{Fe: } [\text{Ar}] 4s^2 3d^6 \]

3. **Nickel (Ni)**: Atomic number = 28
- Electronic configuration: \[ \text{Ni: } [\text{Ar}] 4s^2 3d^8 \]

4. **Copper (Cu)**: Atomic number = 29
- Electronic configuration: \[ \text{Cu: } [\text{Ar}] 4s^2 3d^{10} \]

### Step 2: Determine the electronic configurations of the ions
1. **Zinc ion (Zn²⁺)**:
- Configuration after losing 2 electrons (from 4s): \[ \text{Zn}^{2+}: [\text{Ar}] 3d^{10} \]
- Unpaired d-electrons: **0**

2. **Iron ion (Fe²⁺)**:
- Configuration after losing 2 electrons (first from 4s, then from 3d): \[ \text{Fe}^{2+}: [\text{Ar}] 3d^6 \]
- Filling the d-orbitals:
- 1, 2, 3, 4, 5 (all with the same spin) + 6 (opposite spin)
- Unpaired d-electrons: **4**

3. **Nickel ion (Ni²⁺)**:
- Configuration after losing 2 electrons (first from 4s, then from 3d): \[ \text{Ni}^{2+}: [\text{Ar}] 3d^8 \]
- Filling the d-orbitals:
- 1, 2, 3, 4, 5 (same spin) + 6, 7, 8 (opposite spin)
- Unpaired d-electrons: **2**

4. **Copper ion (Cu²⁺)**:
- Configuration after losing 2 electrons (first from 4s, then from 3d): \[ \text{Cu}^{2+}: [\text{Ar}] 3d^9 \]
- Filling the d-orbitals:
- 1, 2, 3, 4, 5, 6, 7, 8, 9 (1 unpaired)
- Unpaired d-electrons: **1**

### Step 3: Compare the number of unpaired d-electrons
- **Zn²⁺**: 0 unpaired d-electrons
- **Fe²⁺**: 4 unpaired d-electrons
- **Ni²⁺**: 2 unpaired d-electrons
- **Cu²⁺**: 1 unpaired d-electron

### Conclusion
The ion with the maximum number of unpaired d-electrons is **Fe²⁺** with **4 unpaired d-electrons**.

---