Question

ZnO is white when cold and yellow when heated. It is due to the development of

(a) Frenkel defect

(b) metal excess defect

(c) Schottky defect

(d) metal deficiency defect.

Answer 1

Correct option (b) metal excess defect

Explanation:

ZnO tums yellow on heating as Zn²⁺ ions move in interstitial sites and electrons also get entrapped in nearby interstitial sites to maintain electrical neutrality. As extra Zn²⁺ ions are present in interstitial sites thus, it is metal excess defect.