in the cubic packing , the unit cell has ………. .

Options

A. 4 tetrahedral voids each of which is shared by four adjacent unit cells
B. 4 tetrahedral voids within the unit cell
C. 8 tetrahedral voids each of which is shared by four adjacent unit cells
D. 8 tetrahedral voids within the unit cells

Explanation

To solve the question regarding the cubic packing and the number of tetrahedral voids in the unit cell, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Cubic Packing**:
- In cubic packing, particularly in face-centered cubic (FCC) or cubic close packing (CCP), the arrangement of atoms is such that there are specific voids created in the structure.

2. **Identify the Number of Atoms in the Unit Cell**:
- In a face-centered cubic unit cell, there are 4 atoms per unit cell. This is derived from the contribution of atoms at the corners and the faces of the cube.

3. **Calculate the Number of Tetrahedral Voids**:
- The number of tetrahedral voids in a cubic packing is given by the formula:
\[ \text{Number of Tetrahedral Voids} = 2 \times \text{Number of Atoms per Unit Cell} \]
- Substituting the number of atoms:
\[ \text{Number of Tetrahedral Voids} = 2 \times 4 = 8 \]

4. **Determine the Sharing of Tetrahedral Voids**:
- Each tetrahedral void is shared by 4 adjacent unit cells. This means that while there are 8 tetrahedral voids, each void is not entirely contained within a single unit cell but is shared among neighboring cells.

5. **Evaluate the Options**:
- Based on the calculations:
- Option stating "8 tetrahedral voids each of which is shared by 4 adjacent unit cells" is correct.
- Any option suggesting that tetrahedral voids are entirely within a single unit cell is incorrect.

6. **Conclusion**:
- Therefore, the correct answer to the question is that in cubic packing, the unit cell has 8 tetrahedral voids, each shared by 4 adjacent unit cells.