Zinc oxide is white in colour at room temperature but turns yellow when heated on account of

Options

A. metal excess defect due to anionic vacancies
B. metal excess defect due to the presence of extra cations at interstitial sites.
C. metal deficiency defect due to absence of positive ions
D. metal deficiency defect due to extra interstitial negative ions

Answer

2

Explanation

Zinc oxide loses oxygen reversibly at high temperature and turns yellow in colours
`ZnO overset("heating")rarr Zn^(2+)+(1)/(2)O_(2)+2e^(-)`
The excess metal is accommodated interstitially giving rise toe elctrons trappe din the neightbourhood,these electrons absorb energy from the visible light falling on the crystals. giving yellow colour to `ZnO`.
The enhanced electrical conductivity of the nonstoichiometric `ZnO` arises from these electrons.