Assertion : If light is polarised by reflection, then the angle between reflected and refracted ray is `180^@`.
Reason : Brewester's law : `mu = tan i_p`.

Options

A. `pi`
B. `pi//2`
C. `2pi`
D. `pi//4`

Answer

To solve the given problem, we need to analyze the assertion and the reason provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that if light is polarized by reflection, then the angle between the reflected ray and the refracted ray is \(180^\circ\).
- This means that the reflected ray and the refracted ray are in opposite directions.

2. **Analyzing the Situation**:
- When light hits a surface and is polarized by reflection, it follows Brewster's law. At the polarizing angle \(i_p\), the reflected light is completely polarized.
- The angle of incidence \(i_p\) is equal to the angle of reflection \(r\). The angle of refraction \(r'\) can be determined using Snell's law.

3. **Applying Brewster's Law**:
- According to Brewster's law, the relationship between the refractive index \( \mu \) of the medium and the polarizing angle \(i_p\) is given by:
\[ \mu = \tan(i_p) \]
- This means that at the polarizing angle, the reflected and refracted rays are not in opposite directions but rather at a specific angle to each other.

4. **Calculating the Angles**:
- When the light is polarized, the angle between the reflected ray and the refracted ray is actually \(90^\circ\) (not \(180^\circ\)).
- Therefore, the assertion that the angle between the reflected and refracted ray is \(180^\circ\) is incorrect.

5. **Evaluating the Reason**:
- The reason states Brewster's law, which is indeed correct. It provides the correct relationship between the refractive index and the polarizing angle.

6. **Conclusion**:
- Since the assertion is false and the reason is true, we conclude that the correct answer is that the assertion is false and the reason is true.

### Final Answer:
- Assertion: False
- Reason: True