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AIIMS 2017
Exam
AIIMS
Year
2017
Subject
Chemistry
Chapter
Solid State

AIIMS 2017 · Chemistry · Solid State

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

ZnO\mathrm{ZnO} is white when cold and yellow when heated. It is due to the development of

Options

  1. AFrenkel defect
  2. Bmetal excess defect
  3. CSchottky defect
  4. Dmetal deficiency defect.

Correct answer

B. metal excess defect

Step-by-step solution

ZnO\mathrm{ZnO} turns yellow on heating as Zn2+\mathrm{Zn}^{2+} ions move in interstitial sites and electrons also get entrapped in nearby interstitial sites to maintain electrical neutrality. As extra Zn2+\mathrm{Zn}^{2+} ions are present in interstitial sites thus, it is metal excess defect.
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