Read the passage given below and answer the following questions:

Solids are not perfect in structure. There are different types of imperfections or defects in solids. Point defects are of three types:

(I) Stoichiometric defects → Frenkel and Schottky

(II) Non-stoichiometric defects → Metal excess and metal deficient

(III) Impurity defects → caused by the presence of an impurity in the crystal.