Assertion (A) : In the rock salt type structure, all the `OV_(s)` are occupied by `Na^(o+)` ions.
Reason (R ) : Number of `OV_(s) =` Number of `Cl^(ɵ)` ions in the packing.

Options

A. If both `(A)` and `(R)` are correct, and `(R)` is the correct explanation of `(A)`
B. If both `(A)` and `(R)` are correct, but `(R)` is not the correct explanation of `(A)`
C. If `(A)` is correct, but `(R)` is incorrect.
D. If both `(A)` is incorrect but `(R)` is correct.

Explanation

To solve the question, we need to analyze both the Assertion (A) and the Reason (R) provided:

### Step-by-Step Solution:

1. **Understanding the Rock Salt Structure**:
- The rock salt structure refers to the arrangement of sodium chloride (NaCl) in a crystalline form. In this structure, chloride ions (Cl⁻) form a face-centered cubic (FCC) lattice.

2. **Assertion (A)**:
- The assertion states that in the rock salt type structure, all the octahedral voids are occupied by Na⁺ ions.
- In the FCC lattice of Cl⁻ ions, there are octahedral voids created between the Cl⁻ ions. Each octahedral void can indeed be occupied by a Na⁺ ion. Therefore, this assertion is **correct**.

3. **Counting Octahedral Voids**:
- In an FCC lattice, the number of octahedral voids is equal to the number of atoms in the lattice. Since there are 4 Cl⁻ ions in the FCC unit cell (8 corners contributing 1/8 each and 6 face centers contributing 1/2 each), there are also 4 octahedral voids.

4. **Reason (R)**:
- The reason states that the number of octahedral voids equals the number of Cl⁻ ions in the packing.
- As established, in the FCC structure of Cl⁻ ions, there are 4 Cl⁻ ions and 4 octahedral voids. Therefore, this reason is also **correct**.

5. **Relationship Between A and R**:
- While both A and R are correct statements, the reason R does not provide a correct explanation for assertion A. The assertion is about the occupancy of the octahedral voids by Na⁺ ions, while the reason merely states a count of the voids and Cl⁻ ions without explaining why Na⁺ occupies those voids.

6. **Final Conclusion**:
- Since both A and R are correct but R is not the correct explanation of A, the answer is **Option B**: Both A and R are correct, but R is not the correct explanation of A.