Diamond is very hard, because

Options

A. it is covalent solid
B. it has large cohesive energy
C. high melting point
D. insoluble in all solvents

Answer

**Step-by-Step Solution:**

1. **Understanding Diamond Structure:**
- Diamond is a form of carbon where each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. This three-dimensional structure contributes to its hardness.

2. **Covalent Bonds:**
- The bonds between the carbon atoms in diamond are strong covalent bonds. Each bond involves the sharing of electrons between atoms, which creates a very stable and strong interaction.

3. **Cohesive Forces:**
- The cohesive forces in diamond are the attractive forces that hold the atoms together. In diamond, these forces are particularly strong due to the nature of the covalent bonds.

4. **Cohesive Energy:**
- The cohesive energy is the energy required to separate the atoms in a solid. In diamonds, the cohesive energy is very high because of the strong covalent bonds and the tetrahedral arrangement of atoms.

5. **Conclusion:**
- Therefore, diamond is very hard because of the strong covalent bonds between its atoms, the high cohesive forces, and the high cohesive energy resulting from its tetrahedral structure.

**Final Answer:**
Diamond is very hard because it has strong covalent bonds and high cohesive energy due to its tetrahedral atomic arrangement.

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