How would you account for the following?(i) Frenkel defects are not found in alkali metal halides. (ii) Schottky defects lower the density of related solids. (iii) Impurity doped silicon is a semiconductor.

a) Frenkel defects are not shown by the alkali metal halides because the cations cannot get into the interstitial sites as they have larger size.
b) Schottky defect lower the density of the related solid as it is basically a vacancy defect which is produced because of the missing of atoms or ions from their normal crystal.
c) Based on the doping semiconductors are classified into two categories..
1) p-type semiconductors
2) n-type semiconductors
In both the cases, the crystal formed is able to conduct the electricity. So , it is no more an insulator but a semiconductor.