Why does ZnO appear golden yellow at high temperature ? Explain.

Explanation

When ZnO is heated it loses oxygen as :
`ZnO overset("Hea")(rarr) Zn^(2+) + 1/2 O_2 + 2e^(-)`
The `Zn^(2+)` ions are entrapped in the interstitial sites and electrons are entrapped in the neighbouring interstitial sites to maintain electrical neutrality neutrality. This results in metal excess defect. Due to the presence of electrons in the intersitital void, the colour is yellow.