Assertion:In He-Ne lase,Population inversion takes place between energy levels of neon atoms.
Reason:Helium atoms have a meta-stable energy level.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are truw but reason is not correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false.

Explanation

To solve the question, we need to analyze the assertion and the reason provided:

**Assertion:** In He-Ne laser, population inversion takes place between energy levels of neon atoms.

**Reason:** Helium atoms have a metastable energy level.

### Step-by-Step Solution:

1. **Understanding Population Inversion:**
- Population inversion is a condition where a higher number of particles occupy an excited state compared to a lower energy state. This is essential for laser operation.

2. **Analyzing the He-Ne Laser:**
- In a He-Ne laser, a mixture of helium and neon gases is used. When an electric discharge is applied, helium atoms are excited to a metastable energy level.

3. **Helium Metastable State:**
- The metastable state of helium is around 20.61 eV. This state allows helium atoms to remain in an excited state for a longer duration, which is crucial for transferring energy to neon atoms.

4. **Energy Transfer to Neon:**
- The excited helium atoms collide with neon atoms, transferring energy. Neon atoms can then reach an excited state (around 20.66 eV), which is necessary for achieving population inversion.

5. **Population Inversion in Neon:**
- The assertion states that population inversion occurs between the energy levels of neon atoms. This is correct because the excited neon atoms (after energy transfer from helium) have a higher population compared to the lower energy states.

6. **Validity of the Reason:**
- The reason states that helium atoms have a metastable energy level. This is also correct because the metastable state of helium is what allows it to effectively transfer energy to neon atoms, facilitating the population inversion.

7. **Conclusion:**
- Both the assertion and reason are correct, and the reason provides a valid explanation for the assertion. Therefore, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

### Final Answer:
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.

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