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 regarding the assertion and reason about the structure of diamond, let's break it down step by step.

### Step 1: Analyze the Assertion
The assertion states that the number of carbon atoms per unit cell in diamond is 8.

1. **Understanding Diamond Structure**: Diamond has a face-centered cubic (FCC) arrangement. In this arrangement:
- There are 8 corner atoms, each contributing \( \frac{1}{8} \) of an atom to the unit cell.
- There are 6 face-centered atoms, each contributing \( \frac{1}{2} \) of an atom to the unit cell.

2. **Calculating Contribution**:
- Contribution from corner atoms:
\[ 8 \text{ corners} \times \frac{1}{8} = 1 \text{ atom} \]
- Contribution from face-centered atoms:
\[ 6 \text{ faces} \times \frac{1}{2} = 3 \text{ atoms} \]
- Total from FCC arrangement:
\[ 1 + 3 = 4 \text{ atoms} \]

3. **Tetrahedral Voids**: In addition to the atoms in the FCC arrangement, diamond has carbon atoms in tetrahedral voids. The number of tetrahedral voids in an FCC unit cell is double the number of atoms:
- Tetrahedral voids = \( 2 \times 4 = 8 \)
- Since carbon atoms occupy alternate tetrahedral voids, there are 4 additional carbon atoms.

4. **Total Carbon Atoms**:
- Total carbon atoms = 4 (from FCC) + 4 (from tetrahedral voids) = 8.

Thus, the assertion is **true**.

### Step 2: Analyze the Reason
The reason states that the structure of diamond is similar to zinc sulfide (ZnS).

1. **Understanding ZnS Structure**: Zinc sulfide has a similar arrangement:
- ZnS also adopts a cubic close-packed (CCP) structure.
- In ZnS, zinc ions occupy the tetrahedral voids of the FCC arrangement formed by sulfide ions.

2. **Comparison**:
- Both diamond and ZnS have a similar arrangement where one type of atom occupies the tetrahedral voids of the other type of atom arranged in an FCC structure.

Thus, the reason is also **true** and correctly explains the assertion.

### Conclusion
Both the assertion and reason are true, and the reason provides a correct explanation for the assertion. Therefore, the correct answer is:

**Option 1: Both assertion and reason are true, and the reason is the correct explanation of the assertion.**

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