Schottky defect is observed in crystals when __________.
A. some cations move from their lattice site to interstitial sites.

B. equal number of cations and anions are missing from the lattice.

C. some lattice sites are occupied by electrons.

D. some impurity is present in the lattice.

•The Schottky defect is basically a kind of vacancy defect with the tendency to maintain electrical neutrality, therefore same no.s of cations are anions are missing from the crystal lattice.

• Other 3 options are incorrect.

• (i) some of the cations move from their lattice site to interstitial sites – this occurs in the case for Frankel defect only.

• some lattice sites are occupied by electrons- this is the case of metal excess defect.

• (iv) some impurity is present in the lattice – this is observed in crystals with impurity defects.