Which is the incorrect statement?

$\displaystyle \mathrm{FeO}_{0.98}$ has non stoichiometric metal deficiency defect.

Density decreases in case of crystals with Schottky's defect.

$\displaystyle \mathrm{NaCl}(\mathrm{s})$ 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.