When constituent particles are present only on the corner of a unit cell, it is called

Options

A. Primitive unit cell
B. FCC unit cell
C. BCC unit cell
D. All of these

Answer

To solve the question, "When constituent particles are present only on the corner of a unit cell, it is called," we will analyze the options provided and derive the correct answer step by step.

### Step-by-Step Solution:

1. **Understanding Unit Cells**:
- A unit cell is the smallest repeating unit in a crystal lattice. It defines the structure of the entire crystal.

2. **Identifying the Types of Unit Cells**:
- There are different types of unit cells based on the arrangement of constituent particles (atoms, ions, or molecules). The most common types are Primitive (PCC), Face-Centered Cubic (FCC), and Body-Centered Cubic (BCC).

3. **Analyzing the Primitive Unit Cell (PCC)**:
- In a primitive unit cell, constituent particles are located only at the corners of the unit cell.
- Each corner atom contributes 1/8th of its volume to the unit cell because it is shared among eight adjacent unit cells.
- Since there are 8 corners in a cubic unit cell, the total contribution from the corners is:
\[ \text{Total contribution} = 8 \times \frac{1}{8} = 1 \]
- Therefore, the effective number of atoms per unit cell (Z) for a primitive unit cell is 1.

4. **Analyzing the Face-Centered Cubic (FCC)**:
- In an FCC unit cell, atoms are located at the corners and the centers of each face.
- The contribution from the corners is the same as in the primitive unit cell (1 atom), but there are also atoms at the face centers contributing an additional 3 atoms (since each face-centered atom contributes 1/2 to the unit cell).
- Thus, the total effective number of atoms in an FCC unit cell is:
\[ Z = 1 (\text{from corners}) + 3 (\text{from faces}) = 4 \]

5. **Analyzing the Body-Centered Cubic (BCC)**:
- In a BCC unit cell, there is one atom at the center of the cube and atoms at the corners.
- The contribution from the corners is again 1 atom, and the center atom contributes 1 atom.
- Therefore, the effective number of atoms in a BCC unit cell is:
\[ Z = 1 (\text{from corners}) + 1 (\text{from body center}) = 2 \]

6. **Conclusion**:
- Since the question specifically asks for the type of unit cell where constituent particles are present only at the corners, the correct answer is the **Primitive Unit Cell (PCC)**.

### Final Answer:
The correct option is **Primitive Unit Cell (PCC)**.