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 analyze the assertion and reason provided in the question, we can break down the solution into clear steps:

### 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 means that when light reflects off a denser medium (like glass or water), it undergoes a phase shift of π radians (or 180 degrees).

2. **Understanding the Reason**:
- The reason states that "Denser medium is that medium in which speed of wave is less."
- This is true because the speed of light in a medium is inversely related to its refractive index. A higher refractive index indicates a denser medium, where light travels slower.

3. **Analyzing the Reflection**:
- When light travels from a rarer medium (like air) to a denser medium (like glass), it reflects back into the rarer medium.
- During this reflection, the wave undergoes a phase shift of π. This can be understood by considering that the wavefronts change direction and amplitude, leading to this phase change.

4. **Relating Speed and Refractive Index**:
- The speed of light in a medium is given by the formula \( V = \frac{c}{n} \), where \( c \) is the speed of light in vacuum and \( n \) is the refractive index of the medium.
- If \( n_2 > n_1 \) (where \( n_2 \) is the refractive index of the denser medium and \( n_1 \) is that of the rarer medium), then \( V_2 < V_1 \). This confirms that light travels slower in the denser medium.

5. **Conclusion**:
- Both the assertion and the reason are true. However, the reason does not provide the correct explanation for the assertion. The assertion is about the phase change during reflection, while the reason discusses the speed of light in different media.

### Final Answer:
- Both assertion and reason are true, but the reason is not the correct explanation of the assertion.