Which is / are correct statement ?

Options

A. In simple cubic close packed arrangement no octahedral void is present at edge centre.
B. In fcc unit cell octaherdral void and tetrahedral void are vacant .
C. Packing fraction : simple cubic cell `lt` bcc unit cell `lt ` fcc unit cell.
D. Size of void : cubic `gt` octachedral void ` gt` trtrahedral void.

Answer

To determine which statements are correct regarding the solid-state chemistry concepts, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement 1: In simple cubic close pack arrangement, no octahedral void is present at the edge center.**
- In a simple cubic close pack (SCC) arrangement, atoms are located only at the corners of the unit cell. Each corner atom contributes \( \frac{1}{8} \) of an atom to the unit cell, and there are 8 corners, resulting in a total of 1 effective atom per unit cell.
- In this arrangement, there are no octahedral voids at the edge centers, as octahedral voids are formed by the arrangement of atoms in a specific manner, which does not occur in SCC.
- **Conclusion:** This statement is **true**.

2. **Statement 2: In FCC unit cell, octahedral void and tetrahedral voids are vacant.**
- In a face-centered cubic (FCC) unit cell, atoms are located at the corners and the centers of each face. The octahedral voids are formed by the arrangement of six atoms, while tetrahedral voids are formed by four atoms.
- In FCC, while both types of voids exist, they can be vacant if no additional atoms occupy them. The statement does not specify that they are filled, hence it is correct to say they are vacant in this context.
- **Conclusion:** This statement is **true**.

3. **Statement 3: Packing fraction is simple cubic unit cell greater than BCC than FCC.**
- The packing fraction is a measure of how much of the volume of a unit cell is occupied by the atoms.
- Simple cubic (SCC) has a packing fraction of approximately 52.4%.
- Body-centered cubic (BCC) has a packing fraction of about 68%.
- Face-centered cubic (FCC) has a packing fraction of around 74%.
- Therefore, the order of packing fractions is FCC > BCC > SCC, which contradicts the statement.
- **Conclusion:** This statement is **false**.

4. **Statement 4: Size of void is cubic, then octahedral, and then tetrahedral void.**
- The size of the voids can be compared based on the radius ratios:
- Cubic voids can accommodate the largest radius ratio, followed by octahedral voids, and then tetrahedral voids.
- This order is consistent with the radius ratio rules, confirming that cubic voids are indeed the largest, followed by octahedral, and then tetrahedral.
- **Conclusion:** This statement is **true**.

### Final Conclusion:
- The correct statements are:
- Statement 1: **True**
- Statement 2: **True**
- Statement 3: **False**
- Statement 4: **True**

Thus, the correct statements are **1, 2, and 4**.

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