which electronic level allows the hydrogen atom to absorb a photon but not emit a photon?

Options

A. 1s
B. 3s
C. 2p
D. 3d

Answer

To determine which electronic level allows the hydrogen atom to absorb a photon but not emit a photon, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Electronic Levels**:
- In a hydrogen atom, electrons occupy specific energy levels or orbitals, denoted as 1s, 2s, 2p, 3s, etc. The 1s level is the lowest energy level.

2. **Photon Absorption**:
- When a hydrogen atom absorbs a photon, an electron can be excited from a lower energy level to a higher energy level. For example, an electron in the 1s level can absorb a photon and move to the 2s or 3s level.

3. **Photon Emission**:
- After excitation, an electron can return to a lower energy level, which would involve emitting a photon. However, in certain cases, the electron may not return to its original level.

4. **Analyzing the 1s Level**:
- If an electron is in the 1s level and absorbs a photon, it can move to a higher level (e.g., 2s or 3s). However, once it is in the 2s level, it does not have the option to return to the 1s level because it is already in a higher energy state and there are no lower energy states available for it to emit a photon back to.

5. **Conclusion**:
- Therefore, the 1s level allows the hydrogen atom to absorb a photon (to move to a higher energy level) but does not allow it to emit a photon back to the 1s level, as there is no lower energy level available for the electron to return to.

### Final Answer:
The electronic level that allows the hydrogen atom to absorb a photon but not emit a photon is the **1s level**.

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