Which of the following have maximum number of unpaired electrons ?

Options

A. `Na^(+)`
B. `N^(3-)`
C. `Fe^(+2)`
D. `Cr^(3+)`

Explanation

To determine which of the given ions (Na+, N3-, Fe2+, and Cr3+) has the maximum number of unpaired electrons, we need to analyze the electron configurations of each ion. Here’s a step-by-step solution:

### Step 1: Determine the Electron Configuration of Each Ion

1. **Na+ (Sodium Ion)**
- Atomic number of Na = 11
- Electron configuration of neutral Na = 1s² 2s² 2p⁶ 3s¹
- For Na+, one electron is lost from the 3s orbital:
- Electron configuration of Na+ = 1s² 2s² 2p⁶ (10 electrons)
- **Unpaired Electrons in Na+ = 0**

2. **N3- (Nitride Ion)**
- Atomic number of N = 7
- Electron configuration of neutral N = 1s² 2s² 2p³
- For N3-, three electrons are added to the neutral N:
- Electron configuration of N3- = 1s² 2s² 2p⁶ (10 electrons)
- **Unpaired Electrons in N3- = 0**

3. **Fe2+ (Iron Ion)**
- Atomic number of Fe = 26
- Electron configuration of neutral Fe = [Ar] 4s² 3d⁶
- For Fe2+, two electrons are lost from the 4s orbital:
- Electron configuration of Fe2+ = [Ar] 3d⁶ (24 electrons)
- In the 3d subshell, the distribution of electrons is:
- 3d: ↑↓ ↑ ↑ ↑ ↑ (4 unpaired electrons)
- **Unpaired Electrons in Fe2+ = 4**

4. **Cr3+ (Chromium Ion)**
- Atomic number of Cr = 24
- Electron configuration of neutral Cr = [Ar] 4s² 3d⁵
- For Cr3+, three electrons are lost (two from 4s and one from 3d):
- Electron configuration of Cr3+ = [Ar] 3d³ (21 electrons)
- In the 3d subshell, the distribution of electrons is:
- 3d: ↑ ↑ ↑ (3 unpaired electrons)
- **Unpaired Electrons in Cr3+ = 3**

### Step 2: Compare the Number of Unpaired Electrons

- Na+ = 0 unpaired electrons
- N3- = 0 unpaired electrons
- Fe2+ = 4 unpaired electrons
- Cr3+ = 3 unpaired electrons

### Conclusion

The ion with the maximum number of unpaired electrons is **Fe2+** with **4 unpaired electrons**.

### Final Answer:
**Fe2+ has the maximum number of unpaired electrons.**

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