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Which of the following pairs of metals is correctly matched with its commercial extraction method?

1. (Cu, Pb) -> Self reduction
2. (Fe, Zn) -> Electrolytic reduction
3. (Cr, Mg) -> Thermite reduction
4. (Fe, Hg) -> Carbon reduction

Correct answer: (Cu, Pb) -> Self reduction

Solution

Cu and Pb are commercially extracted by self-reduction: their sulfide ores (Cu2S and PbS) are roasted in limited air, producing the metal directly via reactions like Cu2S + O2 -> 2Cu + SO2 and 2PbS + 3O2 -> 2PbO + 2SO2 followed by PbS + 2PbO -> 3Pb + SO2. The other options are incorrect: Fe and Zn use carbon reduction (blast furnace / retort process), Cr uses aluminothermic (thermite) reduction and Mg uses electrolytic reduction, and Hg is extracted by self-reduction not carbon reduction.

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