KEAM 2019 Physics and Chemistry Paper

An example of a non-stoichiometric oxide when heated is ZnO. Zinc oxide is white in colour at room temperature.
On heating, it loses oxygen and turns yellow. Now, there is excess of zinc in the crystal and its formula become Zn1+xO. The excess Zn2+ ions move to interstitial sites and the electron to the neighbouring interstitial sites.