Why does the presence of excess lithium make LiCl crystals pink?

a. The presence of metal excess defects results due to the presence of electrons at the position of negative ions, which results in the generation of F-centers, and the LiCl crystal becomes pink.
b. Effective P atom = 1
Effective Q atom = 18 × 8 = 1
So, the formula of the compound is PQ.