Assertion : The blue colour of sky is on account of scattering of sun light.
Reason : The intensity of scattered light varies inversely as the & fourth power of wavelength of the light.

Options

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

Answer

To determine the validity of the assertion and reason provided in the question, we can break down the statements step by step.

### Step 1: Analyze the Assertion
The assertion states: "The blue colour of the sky is on account of scattering of sunlight."
- **Explanation**: This statement is true. The blue color of the sky is indeed due to Rayleigh scattering, which occurs when sunlight interacts with small particles in the atmosphere. Shorter wavelengths of light (blue light) are scattered more than longer wavelengths (like red light), which is why we perceive the sky as blue during the day.

### Step 2: Analyze the Reason
The reason states: "The intensity of scattered light varies inversely as the fourth power of wavelength of the light."
- **Explanation**: This statement is also true. According to Rayleigh's scattering law, the intensity of scattered light is inversely proportional to the fourth power of the wavelength (λ) of the light. This means that shorter wavelengths (like blue light) are scattered much more than longer wavelengths (like red light). Mathematically, it can be expressed as:
\[ I \propto \frac{1}{\lambda^4} \]
where \(I\) is the intensity of scattered light and \(\lambda\) is the wavelength.

### Step 3: Determine the Relationship
Now we need to determine if the reason is the correct explanation for the assertion.
- Since the assertion is true and the reason is also true, and the reason explains why the blue color of the sky occurs due to the scattering of sunlight (with blue light being scattered more due to its shorter wavelength), we conclude that the reason is indeed a correct explanation of the assertion.

### Conclusion
Both the assertion and reason are true, and the reason correctly explains the assertion. Therefore, the answer is that both statements are true, and the reason is the correct explanation for the assertion.

### Final Answer
Both the assertion and reason are true, and the reason is the correct explanation for the assertion.

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