Which electronic level would allow the hydrogen atom to absorb a photon but not to emit a photon?

Options

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

Answer

To determine which electronic level allows the hydrogen atom to absorb a photon but not to emit one, we need to analyze the quantum numbers associated with each option provided.

### Step-by-Step Solution:

1. **Understanding Photon Absorption and Emission**:
- A hydrogen atom can absorb a photon when it transitions from a lower energy level to a higher energy level. Conversely, it emits a photon when it transitions from a higher energy level to a lower energy level.
- For a level to absorb a photon but not emit one, it must be in a state where it can only absorb energy (i.e., it must be at the ground state or the lowest energy level).

2. **Evaluating Each Option**:
- **Option 1: 3s**
- Principal quantum number (n) = 3
- Azimuthal quantum number (l) for s orbital = 0
- n + l = 3 + 0 = 3
- **Option 2: 2p**
- Principal quantum number (n) = 2
- Azimuthal quantum number (l) for p orbital = 1
- n + l = 2 + 1 = 3
- **Option 3: 1s**
- Principal quantum number (n) = 1
- Azimuthal quantum number (l) for s orbital = 0
- n + l = 1 + 0 = 1
- **Option 4: 3d**
- Principal quantum number (n) = 3
- Azimuthal quantum number (l) for d orbital = 2
- n + l = 3 + 2 = 5

3. **Identifying the Ground State**:
- The ground state of hydrogen is the 1s level (n=1, l=0). This is the lowest energy state.
- Higher energy levels (like 2p, 3s, and 3d) can absorb photons to transition to even higher states but can also emit photons when they return to lower states.

4. **Conclusion**:
- The only level that allows for absorption of a photon without the possibility of emission is the **1s level**. Therefore, the correct answer is **Option 3: 1s**.

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