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

Options

A. Frenkel defect
B. Metal excess defect
C. Metal deficiency defect
D. Schottky defect

Answer

B

Explanation

Zinc oxide is white in colour at room temperature. On heating it loses oxygen and turns yellow.
`ZnO overset("heading") to Zn^(2+) + 1/2 O_(2) + 2e^(-)`
Now there is excess of zinc in the crystal and its formula becomes `Zn_(1+x) O`. The excess `Zn^(2+)` ions move to interstitial sites and the electrons to neighbouring interstitial sites.