Assertion : When light passes from one medium to another of different density the only quantity which is unchanged is its wavelength .
Reason : The wavelength of light is not related to the refractive index of the medium .

Options

A. If both the assertion and reason are true statement and reason is correct explanation of the assertion .
B. If both the assertion and reason are true statement but reason is not a correct explanation of the assertion .
C. If the assertion is true but the reason is a false statement.
D. If both assertion and reason are false statements.

Explanation

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

**Step 1: Understanding the Assertion**
The assertion states that when light passes from one medium to another of different density, the only quantity that remains unchanged is its wavelength.

- When light travels from one medium to another, its speed and wavelength change, but its frequency remains constant. This is because the frequency of light is determined by the source and does not change when light enters a different medium.

**Step 2: Analyzing the Reason**
The reason given is that the wavelength of light is not related to the refractive index of the medium.

- This statement is incorrect. The refractive index (n) of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v). The relationship can be expressed as:
\[ n = \frac{c}{v} \]
- The wavelength (λ) of light in a medium is related to the speed of light in that medium and its frequency (f) by the equation:
\[ v = f \cdot \lambda \]
- When light enters a medium with a different refractive index, its speed changes, and consequently, its wavelength changes as well, while the frequency remains constant.

**Step 3: Conclusion**
Since the assertion is incorrect (the wavelength does not remain unchanged), and the reason is also incorrect (the wavelength is related to the refractive index), we conclude that both the assertion and the reason are false.

### Final Answer:
Both the assertion and the reason are false.

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