density decreases in case of crystals with SCHOTTKYDEFECT NaCl(s) is insulator, silicon is SEMICONDUCTOR, silver is conductor, QUARTZ is piezo-electric crystal Frenkel defect is favoured in those ionic compounds in which sizes of cation and ANIONS are almost equal `FeO_(0.98)` has non-stoichiometric metal deficiency defect
Solution :In Frenkel defect, the radius of cations are smaller than that of anions present in unit cell.