Zinc salts on heating become, yellow, on cooling they again become white. Explain why.

Explanation

Zinc oxide, ZnO on heating lose oxygen reversibly as follows
`ZnO(s)rarrZn^(2+)(s)+2e^(-)+1/(2)O_(2)(g)`
The `Zn^(2+)ande^(-)` are trapped in the interstitial sites. The yellow colour is due to trapped electrons.