In AgBr, there can occur

In AgBr, there can occur

A	only Schottky defect
B	only Frenkel defect
C	Both (a) and (b)
D	Neither (a) nor (b)

Question 7

In an antifluorite structure, cations occupy

A	tetrahedral voids
B	centre of cube
C	octahedral voids
D	corners of cube

Question 8

In Na₂O having antifluorite structureAOxide ions have a cubic close packed arrangement and Na⁺ occupy all the eight tetrahedral voids.BOxide ions have a cubic close packed arrangement and Na⁺ occupy all the octahedral voidsCNa⁺ ions have a cubic close arrangement and O^2– occupy all the octahedral voidsDNa⁺ ions have a cubic close arrangement and O^–2 occupy all the tetrahedral voids

The Correct Answer and Explanation is :

Question 6: Defects in AgBr

• Correct Answer: C (Both Schottky and Frenkel defects)

Explanation:
AgBr (Silver bromide) is an ionic compound that can exhibit both Schottky and Frenkel defects, which are types of point defects in crystals:

1. Schottky Defect:
   A Schottky defect occurs when an equal number of cations and anions are missing from the lattice, creating vacancies. Since AgBr is an ionic solid, the absence of both Ag⁺ and Br⁻ ions from their lattice positions leads to the creation of vacancies. This defect maintains the overall neutrality of the crystal.
2. Frenkel Defect:
   A Frenkel defect occurs when an ion, typically a cation, leaves its normal lattice position and occupies an interstitial site, creating both a vacancy and an interstitial defect. In AgBr, Ag⁺ cations are relatively small, which makes them prone to migrate into interstitial sites, while maintaining the charge neutrality.

Both types of defects can coexist in AgBr, with Schottky defects leading to vacancies and Frenkel defects creating interstitial positions for Ag⁺ ions. This contributes to the compound’s non-stoichiometric nature, where some ions are displaced from their regular positions.

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Question 7: Cations in Antifluorite Structure

• Correct Answer: A (Tetrahedral voids)

Explanation:
The antifluorite structure is an inverse of the fluorite structure. In a fluorite structure, the cations (e.g., Ca²⁺) occupy the tetrahedral voids, and the anions (e.g., F⁻) occupy the cubic close-packed positions.

However, in the antifluorite structure, the positions of cations and anions are reversed. The anions (typically oxide ions, O²⁻) occupy the cubic close-packed arrangement, and the cations (typically alkali metal ions like Na⁺) occupy the tetrahedral voids.

In summary, in the antifluorite structure:

• Anions (O²⁻) are at the cubic close-packed positions.
• Cations (Na⁺) occupy the tetrahedral voids.

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Question 8: Na2O in Antifluorite Structure

• Correct Answer: D (Na⁺ ions have a cubic close arrangement, and O²⁻ occupy all the tetrahedral voids)

Explanation:
In Na₂O (Sodium oxide) with the antifluorite structure:

• O²⁻ ions form a cubic close-packed arrangement.
• The Na⁺ ions occupy all the tetrahedral voids within this arrangement.

In an antifluorite structure, the roles of the cations and anions are reversed compared to the fluorite structure. In fluorite, the larger cations are in the cubic close-packed arrangement, while in antifluorite, the anions (such as O²⁻) occupy those positions. The smaller cations (like Na⁺) occupy the tetrahedral voids between the anions.

Thus, the correct arrangement is that Na⁺ ions are in the tetrahedral voids, and the O²⁻ ions are in the cubic close-packed structure.