Which of the following is the hardest substance?

Options

A. Chromium
B. Rubidium
C. Diamond
D. Iron

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question:**
- The question asks for the hardest substance among the options provided.

2. **Identifying the Hardest Substance:**
- Among known substances, diamond is recognized as the hardest natural material.

3. **Properties of Diamond:**
- Diamond is an allotrope of carbon, which means it is a different structural form of the same element.
- In diamond, carbon atoms are arranged in a tetrahedral structure, forming strong covalent bonds with each other.

4. **Structure of Diamond:**
- The arrangement of carbon atoms in diamond creates a three-dimensional network. This structure contributes to its hardness.
- The covalent bonds in diamond are very strong due to the sharing of electrons between carbon atoms.

5. **Conclusion:**
- Based on the properties and structure of diamond, it is concluded that diamond is the hardest substance known.

6. **Final Answer:**
- Therefore, the correct answer to the question is diamond.

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