Which of the following is/are correct for fluorite structure `(CaF_2)` ?

Options

A. `Ca^(2+)` ions are in ccp with fcc unit cell and `F^-` ions occupy all the tetrahedral voids
B. `Ca^(2+)` ion is surrounded by `4F^-` ions
C. Mass of one unit cell = mass of `4Ca^(2+)` + Mass of `4F^-`
D. C.N. of `F^-`=4 , C.No . `Ca^(2+)`=8

Answer

To determine which statements about the fluorite structure (CaF₂) are correct, we can analyze the structure and the coordination numbers of the ions involved. Here’s a step-by-step breakdown:

### Step 1: Understand the Structure of CaF₂
Calcium fluoride (CaF₂) consists of calcium ions (Ca²⁺) and fluoride ions (F⁻). In this structure, the calcium ions are larger than the fluoride ions.

**Hint:** Remember that in ionic compounds, the size of the ions plays a crucial role in determining the arrangement of the lattice.

### Step 2: Identify the Lattice Arrangement
In the fluorite structure, calcium ions (Ca²⁺) form a face-centered cubic (FCC) lattice. This means that the Ca²⁺ ions occupy the corners and the face centers of the cube.

**Hint:** The FCC arrangement has a specific number of lattice points and coordination numbers associated with it.

### Step 3: Determine Coordination Numbers
- The coordination number of Ca²⁺ ions in the FCC lattice is 8, meaning each Ca²⁺ ion is surrounded by 8 F⁻ ions.
- The fluoride ions (F⁻) occupy the tetrahedral voids in the FCC lattice. Each F⁻ ion is surrounded by 4 Ca²⁺ ions, giving it a coordination number of 4.

**Hint:** Coordination number refers to the number of nearest neighboring ions surrounding a particular ion.

### Step 4: Calculate the Number of Ions per Unit Cell
In an FCC unit cell:
- There are 4 Ca²⁺ ions per unit cell (1/8 from each of the 8 corners + 1/2 from each of the 6 face centers).
- The number of tetrahedral voids is twice the number of atoms in the unit cell, resulting in 8 tetrahedral voids. Thus, there are 8 F⁻ ions per unit cell.

**Hint:** The relationship between the number of atoms and voids is essential for understanding the stoichiometry of the compound.

### Step 5: Analyze the Statements
1. **Statement 1:** "Calcium 2 plus ions are in CCP with FCC unit cell and F minus ions occupy all the tetrahedral voids."
- This statement is **true**.

2. **Statement 2:** "Calcium 2 plus ions are surrounded by 4 F minus ions."
- This statement is **false**; they are surrounded by 8 F⁻ ions.

3. **Statement 3:** "Mass of 1 unit cell is equal to mass of 4 calcium 2 plus plus mass of 4 F minus."
- This statement is **false**; it should be 4 Ca²⁺ and 8 F⁻.

4. **Statement 4:** "The coordination number of F minus is equal to 4."
- This statement is **true**.

### Conclusion
The correct statements regarding the fluorite structure (CaF₂) are:
- Statement 1 is correct.
- Statement 4 is correct.
- Statements 2 and 3 are incorrect.

### Final Answer
**Correct Statements:** 1 and 4.