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Which one of the following metal oxides CANNOT be reduced to the metal by heating with carbon?
A$PbO$
B$ZnO$
C$Al_2O_3$
D$FeO$
Answer & Solution
Correct answer: C. $Al_2O_3$
1. Carbon reduces oxides of moderately reactive metals (Pb, Zn, Fe) at high temperature.
2. Aluminium is highly reactive; $Al_2O_3$ is far more stable than $CO/CO_2$, so carbon cannot reduce it.
3. Aluminium is therefore extracted by electrolysis, not carbon reduction.
_Source: Samacheer Kalvi Class 12 Chemistry Vol.1, Unit 1 'Metallurgy', §1.3.2 / Evaluation Q.4_
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