Which of the following contains only one unpaired electron in the valence shell?

Options

A. `11^(Na)`
B. `21^(Sc)`
C. `9^(F)`
D. `7^(N)`

Answer

To determine which of the given elements contains only one unpaired electron in the valence shell, we will analyze the electronic configurations of each element provided in the options.

### Step-by-Step Solution:

1. **Identify the Elements and Their Atomic Numbers:**
- Option 1: Sodium (Na), Atomic Number = 11
- Option 2: Scandium (Sc), Atomic Number = 21
- Option 3: Fluorine (F), Atomic Number = 9
- Option 4: Nitrogen (N), Atomic Number = 7

2. **Determine the Electronic Configurations:**
- **Sodium (Na)**:
- Atomic Number = 11
- Electronic Configuration: 1s² 2s² 2p⁶ 3s¹
- Valence Shell (3rd shell): 3s¹ (1 unpaired electron)

- **Scandium (Sc)**:
- Atomic Number = 21
- Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹
- Valence Shell (4th shell): 4s² 3d¹ (1 unpaired electron in 3d)

- **Fluorine (F)**:
- Atomic Number = 9
- Electronic Configuration: 1s² 2s² 2p⁵
- Valence Shell (2nd shell): 2s² 2p⁵ (1 unpaired electron in 2p)

- **Nitrogen (N)**:
- Atomic Number = 7
- Electronic Configuration: 1s² 2s² 2p³
- Valence Shell (2nd shell): 2s² 2p³ (3 unpaired electrons in 2p)

3. **Count the Unpaired Electrons in Each Element:**
- Sodium (Na): 1 unpaired electron
- Scandium (Sc): 1 unpaired electron
- Fluorine (F): 1 unpaired electron
- Nitrogen (N): 3 unpaired electrons

4. **Conclusion:**
- The elements that contain only one unpaired electron in their valence shell are Sodium (Na), Scandium (Sc), and Fluorine (F). Nitrogen (N) has 3 unpaired electrons and does not meet the criteria.

### Final Answer:
Sodium (Na), Scandium (Sc), and Fluorine (F) each contain only one unpaired electron in their valence shell.