Directions: For the Assertion (A) and Reason (R) below, choose the correct alternative. Assertion (A): Diamond is used for cutting glass. Reason (R): Diamond has a high refractive index.

Introduction / Context:
This Assertion and Reason question is about the physical properties of diamond and their applications. You must evaluate whether it is correct that diamond is used for cutting glass and whether the stated reason, that diamond has a high refractive index, is the correct explanation. The key is understanding that different properties of diamond are responsible for different uses, such as cutting and optical brilliance.

Given Data / Assumptions:
- Assertion (A): Diamond is used for cutting glass. - Reason (R): Diamond has a high refractive index. - Diamond is known as the hardest natural substance and is also known for its very high refractive index. - Cutting glass requires a material that is harder than glass.

Concept / Approach:
In this type of question, we first judge whether A is true, then whether R is true, and finally whether R correctly explains A. Diamond is indeed used on the tips of glass cutters. However, the property that makes it suitable for cutting is its extreme hardness, not its optical property of having a high refractive index. The refractive index is important for how diamond bends light and appears brilliant, but it does not help in physically cutting glass.

Step-by-Step Solution:
Step 1: Evaluate Assertion (A). It is well known that industrial diamond is used on cutting tools, including glass cutters. Therefore, the assertion that diamond is used for cutting glass is true. Step 2: Evaluate Reason (R). Diamond does indeed have a very high refractive index compared with most other transparent materials. This high refractive index causes strong bending and internal reflection of light, which gives diamond its characteristic sparkle. Therefore, the reason statement is also true as a separate fact. Step 3: Check the explanatory link. The suitability of diamond for cutting glass comes from its exceptional hardness, which allows it to scratch and cut glass surfaces. The refractive index of a material, however, is an optical property that describes how light propagates through it. It has nothing to do with cutting ability or hardness. Thus, R does not provide the correct reason for A. Step 4: We conclude that both A and R are true, but R is not the correct explanation of A.

Verification / Alternative check:
Consider other substances with high refractive index, such as certain heavy flint glasses or liquids. These substances are not used for cutting glass despite their refractive indices because they are not harder than glass. In contrast, some materials that are very hard but have more ordinary refractive indices can be used for cutting. This simple thought experiment shows that hardness, not refractive index, is the essential property for cutting. Therefore, the real explanation for A is diamond's hardness, not its optical behaviour.

Why Other Options Are Wrong:
- It is incorrect to say R is the correct explanation of A, because refractive index is unrelated to cutting ability. - It is incorrect to mark A as false; diamond coated tools for cutting and engraving glass are standard in industry and even in household glass cutters. - It is also incorrect to mark R as false, because diamond really does have a high refractive index. - The option that both A and R are false contradicts established physical facts.

Common Pitfalls:
Some students assume that any true scientific sounding reason must be the explanation of the assertion without checking whether it addresses the relevant physical property. Others mix up optical properties like refractive index with mechanical properties like hardness and strength. To avoid these errors, always ask which property is actually required by the use described in the assertion. If the reason mentions a different property, it may still be true but not the correct explanation.

Final Answer:
Both the assertion and the reason are true statements, but the reason is not the correct explanation of the assertion. The correct choice is therefore Both A and R are true but R is NOT the correct explanation of A.