To determine which of the statements regarding the coordination numbers and unit cells in crystal structures are correct, let's analyze each statement step by step.
### Step 1: Analyze the first statement
**Statement:** The coordination number of each type of iron in C.S.C.L. crystal is 8.
**Analysis:**
- C.S.C.L. stands for cesium chloride, which has a simple cubic lattice structure.
- In a simple cubic structure, each atom is surrounded by 8 other atoms (one at each corner of a cube).
- Therefore, this statement is **correct**.
### Step 2: Analyze the second statement
**Statement:** A metal that crystallizes in B.C.C. structure has a coordination number of 12.
**Analysis:**
- B.C.C. stands for body-centered cubic structure.
- In a B.C.C. structure, each atom at the center is surrounded by 8 corner atoms, leading to a coordination number of 8, not 12.
- Therefore, this statement is **incorrect**.
### Step 3: Analyze the third statement
**Statement:** The coordination number of the B.C.C. structure is 8.
**Analysis:**
- As previously mentioned, in a B.C.C. structure, the coordination number is indeed 8.
- Therefore, this statement is **correct**.
### Step 4: Analyze the fourth statement
**Statement:** The unit cell of an ionic crystal is 12.
**Analysis:**
- This statement is ambiguous. The unit cell of an ionic crystal does not have a fixed coordination number of 12; it depends on the specific ionic compound.
- For example, NaCl has a coordination number of 6, while CsCl has a coordination number of 8.
- Therefore, this statement is **incorrect**.
### Step 5: Analyze the fifth statement
**Statement:** The unit cell of an ionic crystal separates some of its own ions from its other unit cell.
**Analysis:**
- In ionic crystals, ions are arranged in a lattice where certain ions are shared between adjacent unit cells (e.g., corner ions).
- This statement is somewhat vague but can be interpreted as correct because ions do interact with adjacent unit cells.
- Therefore, this statement is **correct**.
### Step 6: Analyze the sixth statement
**Statement:** The length of the edge of the unit cell of NaCl is 552 picometers.
**Analysis:**
- The edge length of the NaCl unit cell can be calculated using the formula: \( a = 2(R_{Na^+} + R_{Cl^-}) \).
- Given \( R_{Na^+} = 95 \) pm and \( R_{Cl^-} = 181 \) pm, we have:
\[
a = 2(95 + 181) = 2 \times 276 = 552 \text{ pm}
\]
- Therefore, this statement is **correct**.
### Conclusion
The correct statements are:
1. The coordination number of each type of iron in C.S.C.L. crystal is 8. (Correct)
2. A metal that crystallizes in B.C.C. structure has a coordination number of 12. (Incorrect)
3. The coordination number of the B.C.C. structure is 8. (Correct)
4. The unit cell of an ionic crystal is 12. (Incorrect)
5. The unit cell of an ionic crystal separates some of its own ions from its other unit cell. (Correct)
6. The length of the edge of the unit cell of NaCl is 552 picometers. (Correct)
### Final Answer:
The correct statements are: 1, 3, 5, and 6.
