Which one is the hardest natural substance among the following?

Options

A. coal
B. coke
C. diamond
D. fullerene

Answer

To determine the hardest natural substance among the options provided (coal, coke, diamond, and fluorine), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Substances**: We have four options:
- A: Coal
- B: Coke
- C: Diamond
- D: Fluorine

2. **Understand the Nature of Each Substance**:
- **Coal**: A combustible black or brownish-black sedimentary rock composed primarily of carbon, along with other elements.
- **Coke**: A solid carbonaceous material derived from heating coal in the absence of air, used mainly in steel production.
- **Diamond**: A form of carbon where each carbon atom is bonded to four other carbon atoms in a three-dimensional tetrahedral structure.
- **Fluorine**: A pale yellow gas at room temperature, it is a highly reactive nonmetal and is not a solid.

3. **Determine Hardness**: Among these substances, we need to evaluate their hardness:
- **Coal and Coke**: Both are relatively soft compared to diamond.
- **Diamond**: Known as the hardest natural substance due to its strong covalent bonds and tetrahedral structure.
- **Fluorine**: As a gas, it does not possess hardness.

4. **Conclusion**: Based on the properties and structures of these substances, diamond is recognized as the hardest natural substance.

### Final Answer:
The hardest natural substance among the options is **C: Diamond**.