Why does `ZnO` show increased electrical conductivity and turns yellow on heating?

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 temperture. On heating it loses oxygenand turns yellow
`ZnOoverset("heating")(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 intrestitial sites and the electrons to neighbouring interstital sites .