The use of diamond as a gem depends on its

Options

A. (a) hardness
B. (b) high refractive index
C. (c) purest form of carbon
D. (d) chemical inertness

Answer

To determine the property of diamond that makes it valuable as a gem, we need to analyze the given options:

1. **Hardness**: Diamonds are known for their exceptional hardness, which makes them resistant to scratching. However, while this is a desirable property for durability, it does not directly contribute to their use as gems in terms of aesthetics or light interaction.

2. **High Refractive Index**: Diamonds have a very high refractive index, which means they can bend light significantly. This property leads to phenomena such as total internal reflection, which is crucial for the sparkle and brilliance of diamonds. The higher the refractive index, the more light is reflected internally, enhancing the gem's appearance.

3. **Purest Form of Carbon**: While diamonds are indeed a pure form of carbon, this purity does not directly influence their aesthetic qualities as a gem. The value of a diamond as a gem is more related to how it interacts with light rather than its chemical composition.

4. **Chemical Inertness**: Diamonds are chemically inert, meaning they do not react easily with other substances. While this contributes to their durability and maintenance, it does not affect their visual appeal as a gem.

Based on this analysis, the use of diamond as a gem primarily depends on its **high refractive index**, which allows for maximum total internal reflection, giving diamonds their characteristic sparkle.

**Final Answer**: The use of diamond as a gem depends on its **high refractive index**.