Which of the following can not change its magnetic moment on excitation ?

Options

A. H
B. Be
C. B
D. O

Answer

To solve the question "Which of the following can not change its magnetic moment on excitation?", we need to analyze the magnetic moments of the given elements based on their electronic configurations. The magnetic moment is determined by the number of unpaired electrons in an atom, which can be calculated using the formula:

\[ \text{Magnetic Moment} = n \times (n + 2) \]

where \( n \) is the number of unpaired electrons.

### Step-by-Step Solution:

1. **Identify the Elements**: The question provides a list of elements (not specified in the question, but we will analyze hydrogen, beryllium, boron, and oxygen based on the transcript).

2. **Analyze Hydrogen**:
- **Electronic Configuration**: Hydrogen (H) has an electronic configuration of \( 1s^1 \).
- **Unpaired Electrons**: It has 1 unpaired electron (n = 1).
- **Excitation**: There is no paired electron to excite, so the number of unpaired electrons remains 1 in both ground and excited states.
- **Conclusion**: The magnetic moment does not change.

3. **Analyze Beryllium**:
- **Electronic Configuration**: Beryllium (Be) has an electronic configuration of \( 1s^2 2s^2 \).
- **Unpaired Electrons**: It has 0 unpaired electrons (n = 0).
- **Excitation**: When one of the paired electrons in the 2s orbital is excited to the 2p orbital, it results in 2 unpaired electrons (n = 2).
- **Conclusion**: The magnetic moment changes.

4. **Analyze Boron**:
- **Electronic Configuration**: Boron (B) has an electronic configuration of \( 1s^2 2s^2 2p^1 \).
- **Unpaired Electrons**: It has 1 unpaired electron (n = 1).
- **Excitation**: When one of the paired electrons in the 2s orbital is excited to the 2p orbital, it results in 3 unpaired electrons (n = 3).
- **Conclusion**: The magnetic moment changes.

5. **Analyze Oxygen**:
- **Electronic Configuration**: Oxygen (O) has an electronic configuration of \( 1s^2 2s^2 2p^4 \).
- **Unpaired Electrons**: It has 2 unpaired electrons (n = 2).
- **Excitation**: When one of the paired electrons in the 2p orbital is excited to a higher energy level, it results in 4 unpaired electrons (n = 4).
- **Conclusion**: The magnetic moment changes.

6. **Final Conclusion**: Based on the analysis, the only element that does not change its magnetic moment upon excitation is **Hydrogen**.

### Answer:
The correct answer is **Hydrogen** (Option 1).