Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R)
Assertion (A) : Refractive index of glass is higher than that of air.
Reason (R) : Optical density of a medium is directly proportionate to its mass density which results in a proportionate refractive index.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. (A) is not correct but (R) is correct
• B. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. Both (A) and (R) are correct but (R) is not the correct explanation of (A)

Hint:

When evaluating Assertion-Reason questions related to physical properties, ensure the Reason provides a direct and accurate explanation for the Assertion. Be wary of generalizations that might not hold true in all cases. Refractive index depends on the interaction of light with the material's electrons, which is more directly related to electron density and atomic structure than just mass density.

Answer 1

The Correct Option is C

The prompt presents one assertion and one reason, requiring an evaluation of their accuracy and interrelation. Let's examine each statement:

1. Assertion (A): "The refractive index of glass exceeds that of air." This statement is accurate. The refractive index quantifies how much light bends upon entering a medium. Glass, being more dense than air, exhibits a higher refractive index (typically around 1.5) compared to air, whose refractive index is approximately 1.
2. Reason (R): "A medium's optical density is directly proportional to its mass density, resulting in a proportional refractive index." This statement is inaccurate. Optical density signifies a material's capacity to decelerate light. While it correlates with refractive index, it is not directly proportional to mass density. A material's refractive index is determined by its electronic structure and bonding, not solely its mass density. Consequently, although denser materials often possess higher refractive indices, this is not a direct proportionality or causation derived exclusively from mass density.

Now, let's assess the relationships to determine the correct option:

• Both (A) and (R) are correct, and (R) correctly explains (A): We have concluded that (R) is an incorrect explanation.
• (A) is incorrect, but (R) is correct: We have verified that (A) is correct, and (R) is incorrect.
• (A) is correct, but (R) is incorrect: This matches our findings. (A) is indeed correct, while (R) is not.
• Both (A) and (R) are correct, but (R) does not correctly explain (A): As (R) is incorrect, this option is invalid.

Therefore, the most fitting answer is: (A) is correct but (R) is not correct.