Question

The type of defect $NaCl$ crystal can exhibit is:

Answer 1

Sodium chloride crystallizes in ccp arrangement. Both sodium and chloride ions are monovalent and of almost similar size. So, they do not exhibit Frenkel defect (in which cations leave their lattice sites and occupy interstitial sites).
But on heating, the bond is broken and an equal number of sodium and chloride ions leave the crystal resulting in vacant cationic and anionic sites.
Thus, sodium chloride on heating shows Schottky defect.

Charateristics of schottky defect:
1. This defect is observed in solids having small difference in the sizes of cations and anions.
2. Solids showing this defect have high coordination numbers.
3. Ion–pair vacancies in this defect decrease the density of the solids.
5. In Schottky defect condition of charge neutrality is maintained.
6. Solids like $NaCl,KCl,AgBr\text{and}CsCl$ show Schottky defects.
Thus, option (a) is correct.