(a) Why does presence of excess of lithium makes LiCl crystals pink ?
(b) A solid with cubic crystal is made of two elements P and Q. Atoms of Q are the corners of the cube and P at the body centre. What is the formula of the compound ?

Explanation

(a) When a crystal of LiCl is present in excess of lithium, the lithium atom loses an `e^(-)` to from `Li^(+)` ions. The released `e^(-)` diffuse into the crystal and occupies the anionic sites (F-centre). These `e^(-)` input the pink colour to the crystal.
(b) We know that in simple cubic number of atoms at corner `(1)/(8) xx 8 = 1` and is also body centre. So the formula of compound is PQ.