For the reduction of given metal oxide to metal, consideration of thermodynamic factors helps in selecting a suitable reducing agent. Ellingham diagrams (plots of Δf​ Go vs T) can predict the feasibility of thermal reduction. Metals with a more negative standard free energy of formation of oxides can reduce the metal oxides with a less negative standard free energy of formation of respective oxides. Metal will reduce the oxides of other metals which lie above it in Ellingham diagram as the standard free energy change for combined redox reaction will be negative by an amount equal to the difference in Δf​Go of two metal oxides. Thus, both Al and Zn can reduce FeO to Fe but Fe cannot reduce Al₂​O₃​ to Al or ZnO to Zn. Also, C can reduce ZnO to Zn but not CO.

(i) Carbon isn't utilized for diminishing aluminum oxide since aluminum is more responsive than carbon. Thus, carbon can't uproot aluminum from its oxide. Aluminum oxide is exceptionally steady and Carbon is less responsive than aluminum, hence it can't be utilized to diminish aluminum oxide to aluminum metal.
(ii) An aqueous solution of sodium chloride is not used for electrolysis because aqueous solution contains water as well which results in the formation of sodium hydroxide in the solution and sodium metal is not obtained.
NaCl(aq) -Electricity- NaOH(aq) + H2(g)(at cathode) + Cl2(g)(at anode)
Hence molten sodium chloride is used to extract sodium from sodium chloride.
NaCl(l) -Electricity-Na(s)(at cathode) + Cl2(g)(at anode)
(iii) The reduction of a metal oxide to form metal by using aluminium powder as a reducing agent is called a thermite reaction. This reduction property of aluminium is used in thermite welding for joining the broken pieces of heavy iron objects like girders, railway tracks or cracked machine parts.

On roasting al these sulphide ores are partly converted into their respective oxides. Since the oxides of mercury and lead are unstable while that of zinc is stable., therefore, oxides of mercury and lead bring about the reduction of their respective sulphides to the corresponding metals but zinc oxides does not reduce ZnS to Zn metal\(\begin{aligned} &\mathrm{HgS}+2 \mathrm{HgO} \stackrel{\Delta}{\longrightarrow} 3 \mathrm{Hg}+\mathrm{SO}_{2} \end{aligned}\) 
             (unstable)
\(\mathrm{PbS}+2 \mathrm{P} \mathrm{bO} \stackrel{\Delta}{\longrightarrow} 3 \mathrm{~Pb}+\mathrm{SO}_{2}\)
               (unstable)
\(\mathrm{ZnS}+\underset{(\text { stable })}{2 \mathrm{ZnO}} \stackrel{\Delta}{\longrightarrow} 3 \mathrm{Zn}+\mathrm{SO}_{2}\)