Assertion : In reflection from a denser medium, any ray of light suffers a phase difference of `pi`.
Reason : Denser medium is that medium in which speed of wave is less.

Options

A. (a) If both Assertion and Reason are true and the Reason is correct explanation of the Assertion.
B. (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
C. (c) If Assertion is true, but the Reason is false.
D. (d) If Assertion is false but the Reason is true.

Answer

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

### Step-by-step Solution:

1. **Understanding the Assertion**:
- The assertion states that "In reflection from a denser medium, any ray of light suffers a phase difference of π."
- This is a well-known property in optics. When light reflects off a denser medium (like from air to glass), it undergoes a phase change of π radians (or 180 degrees). This means that the reflected wave is inverted.

2. **Understanding the Reason**:
- The reason states that "Denser medium is that medium in which speed of wave is less."
- This statement is also correct. In a denser medium, the speed of light (or any wave) is lower compared to a less dense medium. This is due to the properties of the medium affecting how light travels through it.

3. **Analyzing the Relationship**:
- Both the assertion and the reason are correct statements. However, the assertion does not provide an explanation for the phase change in terms of the properties of the medium.
- The phase change of π upon reflection from a denser medium is a result of the boundary conditions of wave behavior at the interface of two different media.

4. **Conclusion**:
- Both the assertion and the reason are correct, but the reason does not explain the assertion. Therefore, while they are both true statements, the assertion is not justified by the reason provided.

### Final Answer:
- **Assertion**: True
- **Reason**: True
- **Conclusion**: The reason does not explain the assertion.