An optically active compound

Options

A. rotates the plane polarised light
B. changes the direction of polarised light
C. does not allow plane polarised light to pass through
D. None of the above

Explanation

To solve the question regarding the behavior of an optically active compound with plane polarized light, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Plane Polarized Light**:
- Plane polarized light consists of waves that vibrate in a single plane. This means that the electric field vectors of the light waves oscillate in one direction.

2. **Definition of Optically Active Compounds**:
- An optically active compound is a substance that can rotate the plane of polarization of plane polarized light when it passes through it.

3. **Behavior of Plane Polarized Light in Optically Active Compounds**:
- When plane polarized light travels through an optically active compound, the plane of polarization is rotated by a certain angle. This rotation is a characteristic property of the compound and depends on factors such as the concentration of the compound and the path length of the light.

4. **Evaluating the Options**:
- **Option A**: "An optically active compound rotates the plane polarized light."
- This statement is true and correctly describes the behavior of optically active compounds.
- **Option B**: "Changes the direction of polarized light."
- This statement is misleading. While the plane of polarization is rotated, the direction of the light itself is not changed.
- **Option C**: "Does not allow plane polarized light to pass through."
- This statement is incorrect. Optically active compounds do allow plane polarized light to pass through; they simply rotate its plane of polarization.
- **Option D**: "None of the above."
- Since Option A is correct, this option is also incorrect.

5. **Conclusion**:
- Based on the evaluation of the options, the correct answer is **Option A**: "An optically active compound rotates the plane polarized light."