Assertion : The frequencies of incident, reflected and refracted beam of monochromatic light are same.
Reason : The incident, reflected and refracted rays are coplanar.

Options

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

Answer

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

### Step 1: Understand the Assertion
The assertion states that "The frequencies of incident, reflected, and refracted beam of monochromatic light are the same."

- **Explanation**: In wave optics, when light passes from one medium to another, the frequency of the light wave remains constant. This is because frequency is determined by the source of the light and does not change when the light enters a different medium.

### Step 2: Understand the Reason
The reason states that "The incident, reflected, and refracted rays are coplanar."

- **Explanation**: Coplanarity means that all three rays (incident, reflected, and refracted) lie in the same plane. This is indeed true according to the laws of reflection and refraction. However, being coplanar does not explain why the frequencies remain the same.

### Step 3: Analyze the Relationship Between Assertion and Reason
Now we need to determine if both statements are true and if the reason correctly explains the assertion.

- **Assertion**: True (frequencies are the same).
- **Reason**: True (the rays are coplanar), but it does not provide a valid explanation for why the frequencies are the same.

### Conclusion
Both the assertion and the reason are true, but the reason does not explain the assertion. Therefore, the final answer is:

- **Assertion is true.**
- **Reason is true, but it is not the correct explanation for the assertion.**

### Final Answer
- Assertion: True
- Reason: True, but not the correct explanation.