Assertion : `CsCI` has body - centred cunic arrangement
Reason: `CsCI` has one and `8 CI^(-)`ion is its unit cell

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false
D. If both assertion and reason are false

Explanation

To solve the question, we need to analyze the assertion and the reason provided regarding the structure of CsCl (cesium chloride).

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that CsCl has a body-centered cubic (BCC) arrangement.
- In a BCC structure, there is one atom at the center of the cube and one atom at each of the eight corners.

2. **Analyzing the Unit Cell of CsCl**:
- In the case of CsCl, the Cs⁺ ion occupies the body center of the cube, while the Cl⁻ ions are located at the corners.
- Each corner of the cube contributes 1/8th of an ion to the unit cell because each corner is shared by eight adjacent cubes.

3. **Counting the Ions in the Unit Cell**:
- There are 8 corners in a cube, and since each corner contributes 1/8th of a Cl⁻ ion, the total contribution of Cl⁻ ions from the corners is:
\[ 8 \times \frac{1}{8} = 1 \text{ Cl}^- \text{ ion} \]
- Additionally, there is 1 Cs⁺ ion at the center of the cube.

4. **Conclusion about the Assertion**:
- The assertion that CsCl has a body-centered cubic arrangement is correct.

5. **Understanding the Reason**:
- The reason states that there is 1 Cs⁺ ion and 8 Cl⁻ ions in the unit cell.
- From our previous calculation, we found that there is only 1 Cl⁻ ion in the unit cell, not 8.

6. **Conclusion about the Reason**:
- The reason provided is incorrect because it misstates the number of Cl⁻ ions in the unit cell.

### Final Conclusion:
- The assertion is true (CsCl has a body-centered cubic arrangement), but the reason is false (there is 1 Cl⁻ ion, not 8).