A : Number of carbon atoms per unit cell in diamond is 8.
R : The structure of diamond is similar to ZnS.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the question, we need to analyze two statements regarding the structure of diamond:

### Step 1: Analyze the first statement
**Statement A**: "The number of carbon atoms per unit cell in diamond is 8."

- Diamond has a face-centered cubic (FCC) structure.
- In an FCC unit cell, the number of atoms (Z) is calculated as follows:
- Each corner atom contributes \( \frac{1}{8} \) of an atom to the unit cell, and there are 8 corners, contributing \( 8 \times \frac{1}{8} = 1 \) atom.
- Each face-centered atom contributes \( \frac{1}{2} \) of an atom, and there are 6 faces, contributing \( 6 \times \frac{1}{2} = 3 \) atoms.
- Therefore, the total number of atoms in an FCC unit cell is \( 1 + 3 = 4 \).

- However, in diamond, each carbon atom is tetrahedrally coordinated, and there are 2 carbon atoms in each tetrahedral void. Since there are 4 tetrahedral voids in the FCC unit cell, the total number of carbon atoms in diamond is \( 4 \times 2 = 8 \).

**Conclusion**: The first statement is true.

### Step 2: Analyze the second statement
**Statement R**: "The structure of diamond is similar to ZnS."

- The structure of diamond is indeed similar to that of zinc blende (ZnS).
- In the zinc blende structure, the sulfur (S) ions form a face-centered cubic lattice, and the zinc (Zn) ions occupy half of the tetrahedral voids.
- Similarly, in diamond, the carbon atoms occupy the tetrahedral voids of the face-centered cubic structure.

**Conclusion**: The second statement is also true.

### Final Conclusion
Both statements A and R are true.

### Summary of the Solution
- Statement A is true: The number of carbon atoms per unit cell in diamond is indeed 8.
- Statement R is true: The structure of diamond is similar to that of ZnS (zinc blende).