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 question provides one assertion and one reason and asks us to evaluate their correctness and relationship. Let's analyze each statement:

1. Assertion (A): "Refractive index of glass is higher than that of air." This assertion is correct. The refractive index of a medium is a measure of how much light is bent, or refracted, when it enters the medium. Glass, being denser than air, has a higher refractive index, typically around 1.5, compared to air, which has a refractive index close to 1.
2. Reason (R): "Optical density of a medium is directly proportionate to its mass density which results in a proportionate refractive index." This reason is not correct. Optical density refers to the ability of a material to slow down light. While it relates to refractive index, it is not directly proportional to mass density. The refractive index of a material depends on the electronic structure and bonding rather than just its mass density. Therefore, while a denser material often has a higher refractive index, this is not a direct proportion or causation due to mass density alone.

Now, let's analyze the relationships to select the correct option:

• Both (A) and (R) are correct and (R) is the correct explanation of (A): We have established that (R) is not a correct explanation.
• (A) is not correct but (R) is correct: We validated that (A) is correct, and (R) is not.
• (A) is correct but (R) is not correct: This aligns with our findings. (A) is indeed correct, while (R) is not.
• Both (A) and (R) are correct but (R) is not the correct explanation of (A): Since (R) is incorrect, this option cannot be chosen.

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

Answer 2

Step 1: Analyze Assertion (A).
Assertion (A) states that the refractive index of glass is higher than that of air. The refractive index of air is approximately 1, and the refractive index of common glass is around 1.5.
Thus, Assertion (A) is correct.
Step 2: Analyze Reason (R).
Reason (R) proposes a direct proportionality between optical density, mass density, and refractive index. While denser materials often have higher refractive indices, this is not a strict direct proportionality and there are exceptions. Optical density depends on the interaction of light with the electrons in the material, which is related to the electron density and atomic structure, not solely mass density.
Therefore, Reason (R) is not correct as a general rule.
Step 3: Determine if Reason (R) is the correct explanation of Assertion (A).
Even if Reason (R) were correct, it provides a general relationship and does not specifically explain why glass has a higher refractive index than air. The reason lies in the different atomic structures and electron densities of glass and air, leading to stronger interaction with light in glass.
Thus, Reason (R) is not the correct explanation for Assertion (A).