Assertion (A) Due to Frenkel defect there is no effect on density of a solid.
Reason`(R)`Ions shift from lattice sites to interstitial sites in Frenkel defect.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true

Answer

To solve the question regarding the assertion and reason related to the Frenkel defect in solids, we will analyze both statements step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that due to the Frenkel defect, there is no effect on the density of a solid.
- To evaluate this, we need to understand what a Frenkel defect is.

2. **Understanding the Frenkel Defect**:
- A Frenkel defect occurs when an ion (usually a cation) leaves its lattice position and occupies an interstitial site within the crystal structure.
- This means that while one ion is missing from its original position in the lattice, it is not lost from the solid; it simply moves to a different location (the interstitial site).

3. **Density Consideration**:
- Density is defined as mass per unit volume. In the case of a Frenkel defect, the total number of ions in the solid remains the same; they are just rearranged.
- Since the mass of the solid does not change (the ion is still present in the solid), and the volume of the solid remains the same (the ion has not left the solid), the density remains unchanged.

4. **Understanding the Reason (R)**:
- The reason states that ions shift from lattice sites to interstitial sites in a Frenkel defect.
- This is accurate as the definition of a Frenkel defect involves the movement of ions from their lattice positions to interstitial positions.

5. **Conclusion**:
- Both the assertion and the reason are correct. The assertion correctly states that there is no effect on density due to the Frenkel defect, and the reason correctly explains the mechanism behind this phenomenon.
- Therefore, the assertion is indeed a correct explanation of the reason.

### Final Answer:
Both the assertion (A) and the reason (R) are correct, and the assertion is the correct explanation of the reason.