Which of the following statements is not correct

Options

A. The number of carbon atoms in an unit cell of Diamond is 4
B. The number of Bravais lattices in which a crystal can be categorized is 14
C. The fraction of the total volume occupied by the atoms in a primitive cell is 0.52
D. Molecular solids are generally volatile

Explanation

To determine which statement is not correct, we need to analyze the statements provided in the context of solid-state chemistry, particularly focusing on the structure of diamond and the properties of unit cells.

### Step-by-Step Solution:

1. **Understanding Diamond Structure:**
- Diamond has a face-centered cubic (FCC) structure.
- Each unit cell of diamond contains 4 carbon atoms.

2. **Analyzing the Statements:**
- **Statement 1:** "The number of atoms in a unit cell of a diamond is 4."
- This statement is correct. In diamond, there are indeed 4 carbon atoms per unit cell.

- **Statement 2:** "There are 14 Bravais lattices."
- This statement is also correct. There are 14 distinct Bravais lattices in three-dimensional space.

- **Statement 3:** "The fraction of the total volume occupied by the atoms in a primitive cell is 0.52."
- This statement is misleading. The packing fraction for a simple cubic structure is approximately 0.52, but for diamond, which has a more complex structure, the packing fraction is lower. Therefore, this statement is not correct.

3. **Conclusion:**
- The statement that is not correct is the one regarding the fraction of the total volume occupied by the atoms in a primitive cell being 0.52. The correct packing fraction for diamond is lower than this value.

### Final Answer:
The statement that is not correct is: "The fraction of the total volume occupied by the atoms in a primitive cell is 0.52."