JEE Main · 2014 · 06 Apr 2014 · Offline · General Principles and Processes of Isolation of Metals

Follow the iron through each route. Heating iron in oxygen gives the mixed oxide $\mathrm{Fe}{}_3\mathrm{O}{}_4$; carbon monoxide then reduces it stepwise, to $\mathrm{FeO}$ near $600^{\circ }$C and on to metallic $\mathrm{Fe}$ near $700^{\circ }$C, exactly the chemistry of the blast furnace. The other routes fail: $\mathrm{FeCl}{}_3$ is not turned into $\mathrm{FeCl}{}_2$ by heating in air, and heating $\mathrm{Fe}{}_2(\mathrm{SO}{}_4){}_3$ or $\mathrm{FeSO}{}_4$ yields iron oxides rather than the free metal. The sound sequence is $\mathrm{Fe}\to \mathrm{Fe}{}_3\mathrm{O}{}_4\to \mathrm{FeO}\to \mathrm{Fe}$.