Assertion:Frenkel defect is also called dislocation defect
Reason:Frenkel defect is shown by ionic substances in which cation and anion are of almost similar sizes.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false
D. If both assertion and reason are false

Explanation

To analyze the assertion and reason provided in the question, we can break it down into a step-by-step solution:

### Step 1: Understand the Assertion
The assertion states that "Frenkel defect is also called dislocation defect."

**Explanation:**
Frenkel defect is indeed a type of point defect in a crystal lattice where an atom or ion is displaced from its normal lattice position to an interstitial site. This displacement creates a vacancy at the original site and an interstitial defect at the new site. Due to this nature of displacement, it is often referred to as a dislocation defect.

### Step 2: Understand the Reason
The reason states that "Frenkel defect is shown by ionic substances in which cation and anion are of almost similar sizes."

**Explanation:**
Frenkel defects typically occur in ionic compounds where there is a significant size difference between the cations and anions. This is because the smaller cation can fit into the interstitial sites of the larger anion lattice. Therefore, the reason provided is incorrect as it misrepresents the conditions under which Frenkel defects occur.

### Step 3: Conclusion
Based on the analysis:
- The assertion is **true**: Frenkel defect is indeed called a dislocation defect.
- The reason is **false**: Frenkel defects occur in ionic compounds where there is a significant size difference between cations and anions, not when they are of almost similar sizes.

### Final Answer
- **Assertion:** True
- **Reason:** False