Which of the elements shows both Schottky and Frenkel Defects?

AgBr

The answer is 3. AgBr.

AgBr shows both Schottky and Frenkel defects.

Schottky defects occur when equal numbers of cations and anions are missing from their lattice sites. This defect is common in crystals with similar sized ions, such as NaCl.

Frenkel defects occur when an atom or ion leaves its regular lattice site and occupies an interstitial position, creating a vacancy at the original lattice site. This defect is common in crystals with large ions, such as AgBr.

The radius ratio of AgBr is 0.78, which is intermediate between the values for NaCl (0.55) and CsCl (0.86). This means that AgBr can exhibit both Schottky and Frenkel defects.

NaBr shows only Schottky defects, and CsCl shows only Frenkel defects.