Which of the following contains rock salt structure?

Options

A. `SrF_(2)`
B. MgO
C. `AI_(2)O_(3)`
D. All of these

Answer

To determine which of the given compounds contains a rock salt structure, we need to understand the characteristics of the rock salt structure, also known as the NaCl type structure.

### Step-by-Step Solution:

1. **Understanding Rock Salt Structure**:
- The rock salt structure is characterized by a face-centered cubic (FCC) arrangement of anions (usually larger ions) with cations (usually smaller ions) occupying the octahedral voids.
- The ratio of the radius of the cation to the radius of the anion (R+ / R-) is crucial. For the rock salt structure, this ratio should be greater than 0.414 but less than 0.732.

2. **Identifying the Compounds**:
- Let's consider the compounds in question: NaCl, MgO, and others mentioned in the transcript.
- We will analyze the ionic radii of the cations and anions in these compounds.

3. **Analyzing NaCl**:
- Na+ has a radius of approximately 1.02 Å and Cl- has a radius of approximately 1.81 Å.
- The ratio R+ / R- = 1.02 / 1.81 ≈ 0.564, which is within the range (0.414 < 0.564 < 0.732). Thus, NaCl has a rock salt structure.

4. **Analyzing MgO**:
- Mg2+ has a radius of approximately 0.72 Å and O2- has a radius of approximately 1.40 Å.
- The ratio R+ / R- = 0.72 / 1.40 ≈ 0.514, which is also within the range (0.414 < 0.514 < 0.732). Therefore, MgO also has a rock salt structure.

5. **Analyzing Other Compounds**:
- The transcript mentions SrF2 and Al2O3.
- SrF2 has a different structure (anti-fluorite) and Al2O3 does not have a rock salt structure.
- Therefore, they do not qualify as having a rock salt structure.

6. **Conclusion**:
- From the analysis, both NaCl and MgO exhibit the rock salt structure.

### Final Answer:
The compounds that contain a rock salt structure are **NaCl and MgO**.