Question

Assertion: Due to Frenkel defect, density of the crystalline solid decreases.
Reason: In Frenkel defect, cation and anion leaves the crystal.

• A. Assertion is true but Reason is false.
• B. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
• C. Both Assertion and Reason are false.
• D. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Hint:

To remember the density effects: - Frenkel: "Friend stays inside" → Density Same. - Schottky: "S" for "Small/Subtract" → Ions leave → Density Decreases.

Answer 1

The Correct Option is C

Concept: The Frenkel defect is a type of point defect in crystalline solids where an ion (usually the smaller cation) is displaced from its normal lattice site to an interstitial site. Key characteristics: • It is a dislocation defect. • The total number of ions in the crystal remains unchanged. • It occurs in compounds where there is a large difference in the size of cations and anions (e.g., AgCl, AgBr, ZnS).
In a Frenkel defect, the ion simply moves from one position to another within the same crystal. No ions are lost to the surroundings. Since the mass and the volume of the crystal remain constant, the density does not change. Therefore, the Assertion is false.
The statement that "cation and anion leaves the crystal" describes a Schottky defect, not a Frenkel defect. In a Frenkel defect, the ions remain inside the crystal at interstitial positions. Therefore, the Reason is also false.