Why carbon exists as the hardest crystalline solid, though it is a non metal?

Explanation

### Step-by-Step Solution:

1. **Understanding Carbon's Allotropes**:
- Carbon exists in several allotropic forms, including coal, graphite, and diamond. Among these, diamond is known as the hardest crystalline solid.

2. **Identifying the Structure of Diamond**:
- Diamond has a unique structure where each carbon atom is sp³ hybridized. This means that each carbon atom forms four equivalent covalent bonds with four other carbon atoms.

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