Question

Assertion (A): In a particular point defect, an ionic solid is electrically neutral, even if few of its cations are missing from its unit cells.
Reason(R): In an ionic solid, Frenkel defect arises due to dislocation of cation from its lattice site to interstitial site, maintaining overall electrical neutrality.
Choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct and (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Crystals maintain electrical neutrality regardless of defects.
Point defects include stoichiometric defects like Schottky (missing ions) and Frenkel (displaced ions).
Step 2: Detailed Explanation:
Evaluation of Assertion (A):
In ionic solids, when cations are missing (as in a Schottky defect), neutrality is maintained because an equal number of anions are also missing. In metal-excess defects, electrons might occupy the vacancy (F-centers). Thus, the solid remains neutral.
The assertion is True.

Evaluation of Reason (R):
In a Frenkel defect, a cation moves from its original site to an empty "interstitial" space between the other ions. Since no charges are added or removed, neutrality is perfectly maintained.
The reason is True.

Conclusion:
While both statements are correct, Reason (R) describes a dislocation defect (nothing missing). Assertion (A) specifically mentions missing cations.
The mechanism for neutrality in a Schottky defect (equal anion loss) is different from the mechanism in a Frenkel defect (dislocation).
Therefore, R is not the explanation for A.
Step 3: Final Answer:
Both (A) and (R) are correct, but (R) is not the correct explanation of (A).