Assertion:- Different colours of light have same velocity in vaccum, but they have differnet velocites in any other transparent medium.
Reason:- For different colours, refractive index of transparent medium has different values.

Options

A. If both Assertion `&` Reason are True `&` the Reason is a correct explanation of the Assertion.
B. If both Assertion `&` Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion `&` Reason are False.

Answer

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

### Step 1: Understand the Assertion
The assertion states that "Different colours of light have the same velocity in vacuum, but they have different velocities in any other transparent medium."

- **Explanation**: In a vacuum, all colors of light travel at the same speed, which is the speed of light (approximately \(3 \times 10^8\) m/s). However, when light travels through a medium (like glass or water), its speed changes depending on the wavelength (or color) of the light. This is due to the phenomenon of refraction.

### Step 2: Understand the Reason
The reason states that "For different colours, the refractive index of the transparent medium has different values."

- **Explanation**: The refractive index \(n\) of a medium is defined as the ratio of the speed of light in vacuum to the speed of light in the medium. Different colors of light have different wavelengths, and thus they interact differently with the medium, leading to different refractive indices. This difference in refractive index causes different colors of light to travel at different speeds in the medium.

### Step 3: Conclusion
Both the assertion and reason are true. The assertion is correct because it accurately describes the behavior of light in vacuum and in other media. The reason is also correct because it explains why different colors of light have different velocities in a medium due to varying refractive indices.

### Final Answer
- **Assertion**: True
- **Reason**: True
- **Explanation**: The reason is a valid explanation for the assertion.

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