$\begin{array}{1 1} (1) FeO_{0.98} \text{has non stoichiometric metal
deficienry defect} \\ \text{(2) Density decreases in case of crystals with
Schottky's defect.} \\
(3) NaCI(G) \text{is insulator, silicon is semiconductor,
silver is conductor, quartz is piezo electric
crystal.} \\ \text{(3)
Frenkel defect is favoured in those ionic
compounds in which sizes of cation and
aniors are almost equal.} \end{array} $
