Which kind of defect is observed in AgBr ?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Both Frenkel and Schottky defects
In ionic solids there are two kinds of stoichiometric point defects:
Schottky defect: an equal number of cations and anions are missing from their sites. It is shown by ionic solids whose cations and anions are of almost the same size (NaCl, KCl, CsCl), and it lowers the density.
Frenkel defect: a smaller ion (usually the cation) leaves its site and occupies an interstitial site. It is shown when there is a large difference in the size of the ions (ZnS, AgCl, AgBr, AgI), and it does not change the density.
AgBr is the substance that shows both Frenkel and Schottky defects: the small \( \ce{Ag+} \) ion can move into interstitial sites, and pairs of \( \ce{Ag+} \) and \( \ce{Br-} \) ions can also be missing.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Schottky Defect – …
