Zine oxide is white but it turns yellow on heating . Explain.

Explanation

When ZnO is heated, it loses oxygen according to the reaction :`ZnO to Zn^(2+) + 1/2O_2 + 2e^(-)`
`Zn^(2+)` ions are entrapped in the interstitial voids and electrons in the neighbouring interstitial voids to maintain electrical neutrality. This gives rise to metal defect. Due to presence of electron in the interstitial voids (F-centres), the colour is yellow as the remaining colours of white light are absorbed by these electrons.