Which of the following statements is not correct ?

Options

A. The number of carbon atoms in the unit cell of diamond is 4
B. The number of Bravais lattics in which a crystal can be catagorized is 14
C. The fraction of the total volume occupied by the atoms in a primitive cell is `0.48`
D. Molecular solids are generally volatile

Explanation

To solve the question "Which of the following statements is not correct?", we will analyze each statement provided in the question regarding solid-state chemistry, particularly focusing on diamond structure and related concepts.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- The first statement claims that the number of carbon atoms in the unit cell of diamond is four.
- In diamond, the structure is based on a face-centered cubic (FCC) arrangement of carbon atoms. Each corner of the cube contributes 1/8 of an atom, and there are 8 corners, contributing a total of 1 atom. Additionally, there are 6 face centers, each contributing 1/2 of an atom, contributing a total of 3 atoms.
- Furthermore, there are 4 carbon atoms located in the alternate tetrahedral voids.
- Thus, the total number of carbon atoms in the diamond unit cell is 1 (from corners) + 3 (from face centers) + 4 (from tetrahedral voids) = 8 atoms.
- Therefore, the statement that the number of carbon atoms in the unit cell of diamond is four is **incorrect**.

2. **Analyze the Second Statement:**
- The second statement claims that the number of Bravais lattices in which a crystal can be categorized is fourteen.
- This is correct. In three-dimensional space, there are indeed 14 distinct Bravais lattices that categorize crystal structures.

3. **Analyze the Third Statement:**
- The third statement states that the fraction of total atoms occupied by the atoms in a primitive cell is 0.48.
- This is also correct. The packing fraction for a simple cubic unit cell is calculated to be 0.52, which means the fraction of free space is 1 - 0.52 = 0.48.

4. **Analyze the Fourth Statement:**
- The fourth statement claims that molecular solids are generally volatile.
- This is true as well. Molecular solids have weak intermolecular forces, which often lead to higher volatility compared to ionic or covalent solids.

### Conclusion:
After analyzing all statements, we conclude that the first statement is the only incorrect one.

**Final Answer:**
The statement that is not correct is: **The number of carbon atoms in the unit cell of diamond is four.**

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