Pick out correct statements regarding ZnO

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It becomes yellow on heating due to development of metal excess defects in crystal

It becomes yellow on heating due to development of metal deficiency defects in crystal

Non- stoichiometric ZnO is n-type semiconductor

When non – stoichiometric ZnO is heated in O2 and then cooled to room temperature, its conductivity decreases

answer is A.

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Detailed Solution

ZnO looses oxygen reversibly at high temperature and turns yellow in color. The excess metal is accommodated interstial, giving rise two electrons trapped in the neighborhood. The enhanced electrical conductivity of the non-stoichiometric ZnO arises from these electrons (n-type conductor)ZnOS⇌Zns2++12O2g+anion vaccancy +2e−. When non-stoichiometric ZnO is heated is dioxygen,O2 oxides some of the interstitial ions, and these subsequently remove interstitial electrons, which reduces the conductivity .

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