A unit cell of `BaCl_2` (fluorite structure) is made up of

Options

A. four `Ba^(2+)` ions and four `Cl^-` ions
B. four `Ba^(2+)` ions and eight `Cl^-` ions
C. eight `Ba^(2+)` ions and four `Cl^-` ions
D. four `Ba^(2+)` ions and six `Cl^-` ions

Explanation

To determine the composition of the unit cell of barium chloride (BaCl₂) in a fluorite structure, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure**: Barium chloride (BaCl₂) adopts a fluorite structure. In this structure, the barium ions (Ba²⁺) occupy the face-centered cubic (FCC) lattice positions, while the chloride ions (Cl⁻) occupy the tetrahedral voids.

2. **Identify the Number of Ions in the Unit Cell**:
- In a face-centered cubic unit cell, there are 4 whole atoms (ions) per unit cell. This is derived from the fact that each corner atom contributes 1/8th to the unit cell and each face-centered atom contributes 1/2.
- For BaCl₂, the barium ions are present at the lattice points, and since there are 4 barium ions in the unit cell, we can conclude that there are 8 barium ions in the complete structure.

3. **Calculate the Number of Chloride Ions**:
- In the fluorite structure, for every 1 barium ion, there are 2 chloride ions to maintain charge neutrality (Ba²⁺ requires two Cl⁻ ions).
- Since there are 4 barium ions in the unit cell, the number of chloride ions will be 4 × 2 = 8 chloride ions.

4. **Conclusion**: Therefore, the unit cell of barium chloride (BaCl₂) in a fluorite structure contains 8 barium ions and 4 chloride ions.

### Final Answer:
The unit cell of BaCl₂ (fluorite structure) is made up of **8 barium ions and 4 chloride ions**.

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