Assertion: Blue light travels slower than red light in vacuum.
Reason : Frequency of blue light is greater than that of red light.

Options

A. If both assertion and reason are correct and rason is a correct explanation of the assertion.
B. If both assertion and reason are correct but reason is not the correct explanation of assertion.
C. If assertion is correct but reason is incorrect.
D. If assertion is incorrect but reason is correct.

Answer

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

### Step 1: Understand the Assertion
The assertion states that "Blue light travels slower than red light in vacuum."

- In physics, particularly in optics, it is known that the speed of light in a vacuum is constant for all colors of light. This speed is approximately \(3 \times 10^8\) meters per second.
- Therefore, the assertion is incorrect because all colors of light, including blue and red, travel at the same speed in a vacuum.

### Step 2: Understand the Reason
The reason states that "Frequency of blue light is greater than that of red light."

- It is a known fact that blue light has a higher frequency compared to red light. The frequency and wavelength of light are inversely related, meaning that as the frequency increases, the wavelength decreases.
- Since blue light has a shorter wavelength than red light, its frequency is indeed greater. Thus, the reason is correct.

### Step 3: Conclusion
Now, we can summarize our findings:
- The assertion is incorrect because blue light does not travel slower than red light in a vacuum; they both travel at the same speed.
- The reason is correct because the frequency of blue light is indeed greater than that of red light.

### Final Answer
Based on the analysis, the correct answer is that the assertion is incorrect, while the reason is correct. Therefore, the answer is D.

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