In the fluorite structure, the coordination number of cation is:

Options

A. 4
B. 6
C. 8
D. 3

Answer

To determine the coordination number of cations in the fluorite structure (specifically in CaF2), we can follow these steps:

### Step 1: Understand the Structure
The fluorite structure is characterized by the arrangement of cations (Ca²⁺) and anions (F⁻). In this structure, the calcium ions are larger than the fluoride ions.

**Hint:** Familiarize yourself with the basic structure of fluorite, which consists of cations and anions arranged in a specific geometric pattern.

### Step 2: Identify the Coordination Number
The coordination number refers to the number of nearest neighbor ions surrounding a central ion. For cations in the fluorite structure, we need to determine how many fluoride ions surround each calcium ion.

**Hint:** Coordination number can be visualized as how many ions are directly adjacent to a central ion.

### Step 3: Analyze the Arrangement
In the fluorite structure, the Ca²⁺ ions occupy the face-centered cubic (FCC) lattice positions. The F⁻ ions occupy all the tetrahedral voids within this FCC lattice.

**Hint:** Remember that in FCC, each corner atom is shared among 8 unit cells, and face-centered atoms are shared between 2 unit cells.

### Step 4: Count the Nearest Neighbors
For each Ca²⁺ ion located at the corners and face centers of the FCC lattice, it is surrounded by F⁻ ions located in the tetrahedral voids. Each Ca²⁺ ion has 8 F⁻ ions as its nearest neighbors.

**Hint:** Visualize the geometry; tetrahedral voids are positioned such that they can be surrounded by four ions, but in the case of Ca²⁺, it effectively touches 8 F⁻ ions due to the arrangement.

### Step 5: Conclusion
Thus, the coordination number of the cation (Ca²⁺) in the fluorite structure is 8.

**Final Answer:** The coordination number of cation (Ca²⁺) in the fluorite structure is **8**.

---