Question

Which of the following oxide cannot be reduced with carbon to obtain the metal.

• A. ${MnO}_2$
• B. ${Cr}_2{O}_3$
• C. ${Al}_2{O}_3$
• D. None of these

Answer 1

The correct option is D

None of these

Explanation for the correct option:

D

• Reducing agents are the species that reduces other substance but gets oxidized in the reaction.
• Arrangement of the metals on the basis of their reactivity towards other elements is termed as activity series. The activity series in decreasing order is:

$\mathrm{K}>\mathrm{Na}>\mathrm{Li}>\mathrm{Ba}>\mathrm{Sr}>\mathrm{Ca}>\mathrm{Mg}>\mathrm{Al}>\mathrm{Mn}>\mathrm{Zn}>\mathrm{Cr}>\mathrm{Fe}>\mathrm{Cd}>\mathrm{Co}>\mathrm{Ni}>\mathrm{Sn}>\mathrm{Pb}>\mathrm{H}>\mathrm{Sb}>\mathrm{Bi}>\mathrm{Cu}>\mathrm{Hg}>\mathrm{Ag}>\mathrm{Au}>\mathrm{Pt}$

• Elements at the starting of this series are comparatively more reactive than elements present after them in the series.
• Manganese dioxide $\left({\mathrm{MnO}}_2\right)$, Chromium(III) oxide $\left({\mathrm{Cr}}_2{\mathrm{O}}_3\right)$, and Aluminium oxide $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ are the oxides of reactive metals Manganese $\left(\mathrm{Mn}\right)$, Chromium $\left(\mathrm{Cr}\right)$ and Aluminium $\left(\mathrm{Al}\right)$ respectively.
• Since Carbon $\left(\mathrm{C}\right)$ is not a strong reducing agent, it cannot reduce the oxides of these reactive elements.

Hence, option D is correct.