(a) When a crystal of LiCl is heated in an atmosphere of Li vapour, the Li atoms lose electron to for `Li^(+)` ions. The released electrons diffuse into the crystal and occupy anionic sites. These electrons impact pink colour to the LiCl crystal.
(b) It is given that the atoms of Q are present at the corners of the cube.
Therefore, number of atoms of Q in one unit cell `=8xx(1)/(8)=1`.
It is also given that the atoms of P are present at the body-centre. Therefore, numbers of atoms of P in one unit cell = 1. This means that the ratio of the number of Q atoms P: Q = 1 : 1.
Hence, the formula of the compound is PQ.