Which of the following unit cells has constituent particles occupying the corner positions only ?

Options

A. Body-centered cell
B. Primitive cell
C. Face centered cell
D. End-centered cell

Answer

To determine which unit cell has constituent particles occupying only the corner positions, we need to analyze the types of unit cells and their arrangements.

### Step-by-Step Solution:

1. **Understanding Unit Cells**:
- A unit cell is the smallest repeating unit in a crystal lattice that shows the entire structure's symmetry and arrangement.
- There are several types of unit cells, including simple cubic (SC), body-centered cubic (BCC), face-centered cubic (FCC), and others.

2. **Analyzing Simple Cubic (SC) Unit Cell**:
- In a simple cubic unit cell, there are atoms located only at the corners of the cube.
- Each corner atom is shared among eight adjacent unit cells, contributing 1/8 of an atom to the unit cell.
- Therefore, in a simple cubic unit cell, the total number of atoms is \(8 \times \frac{1}{8} = 1\).

3. **Analyzing Body-Centered Cubic (BCC) Unit Cell**:
- In a BCC unit cell, there are atoms at the corners and one atom at the center of the cube.
- Since there is an atom in the center, this unit cell does not have constituent particles occupying only the corners.

4. **Analyzing Face-Centered Cubic (FCC) Unit Cell**:
- In an FCC unit cell, there are atoms at the corners and additional atoms at the centers of each face of the cube.
- Thus, this unit cell also does not have constituent particles occupying only the corners.

5. **Conclusion**:
- The only unit cell that has constituent particles occupying the corner positions only is the **Simple Cubic (SC)** unit cell.

### Final Answer:
The unit cell that has constituent particles occupying the corner positions only is the **Simple Cubic (SC) unit cell**.

---