Why does white zinc oxide on heating become yellow ?

Assertion (A): Nitric oxide on heating becomes yellowish brown in colour. Reason (R): On oxidation NO oxidises into yellow brown coloured NO_2 .

Which of the following metal oxide is white in colour but become yellow on heating

Which of the following metal oxides is white in colour but becomes yellow on heating

What is crystal defects? Why ZnO when heated becomes yellow?

Why does sodium chloride on heating with sodium vapours acquire yellow colour ?