Which of the following statements is not correct ?

Options

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

Answer

To determine which statement is not correct, we will analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement:** There are 14 Bravais lattices.
**Analysis:** This statement is correct. In solid-state physics, there are indeed 14 distinct Bravais lattices that describe the different ways in which points can be arranged in three-dimensional space.

### Step 2: Analyze the Second Statement
**Statement:** The packing fraction of a simple cubic unit cell is 52.4%.
**Analysis:** This statement is also correct. The packing fraction, which is the fraction of volume in a unit cell that is occupied by the atoms, for a simple cubic unit cell is approximately 52.4%. This is calculated based on the volume of the atom and the volume of the unit cell.

### Step 3: Analyze the Third Statement
**Statement:** Molecular solids are generally volatile because they have weak intermolecular forces.
**Analysis:** This statement is correct. Molecular solids typically have weak intermolecular forces, which allows them to exist as liquids or gases at room temperature, making them volatile.

### Step 4: Analyze the Fourth Statement
**Statement:** The number of carbon atoms in the unit cell of diamond is four.
**Analysis:** This statement is incorrect. Diamond has a face-centered cubic (FCC) structure, which contains 4 carbon atoms per unit cell. However, in diamond, there are additional carbon atoms located in the tetrahedral voids, leading to a total of 8 carbon atoms in the diamond structure, not just 4.

### Conclusion
The statement that is not correct is the fourth one: "The number of carbon atoms in the unit cell of diamond is four."

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