Question

ZnO crystal on heating acquires the formula $Z{n}_{1+X}O$. Give reason.

Answer 1

$1.$On heating $ZnO$, it loses oxygen and there is excess of $Z{n}^{2+}$ ions in the crystal.
$2.$ On heating $ZnO$ changes to yellow from white powder. When you heat $ZnO$ then Oxygen leaves as $O_2$
leaving behind $Z{n}^{2+}$ and $2$ electrons.
$3.$$Z{n}^{2+}$ and the $2$ electrons move to the interstitial sites of the crystal . This provides excess electrons in
the crystal lattice of $ZnO$.
4.When light falls on these crystals then these electrons absorb a part of the light in the visible region
and hence impart a yellow colour to the $ZnO$.