Which one is the incorrect statement ?
a. FeO0.98 has non-stoichiometric metal deficiency defect
b. Density decreases in case of crystals with Schottky's defect
c. NaCl(s) is insulator, silicon is semiconductor, silver is conductor, quartz is piezo electric crystal
d. Frenkel defect is favoured in those ionic compounds in which sizes of cations and anions are almost equal