Give reason :
(a) Why is Frenkel defect found in AgCl ?
(b) What is the difference between silicon doped with phosphorus and doped with gallium semi-conductors ?

Explanation

Size of `Ag^(+)` ions is very small. They can easily leave their normal sites in the crystal lattice and occupy positions elsewhere in the latice. This leads to Frenkel defect.
(b) Silicon doped with phosphorus gives n-type semi-conductor while silicon doped with gallium leads to p-type semi-conductor.