Lead is extracted from galena $(\mathrm{PbS})$, either by following ways. Auto-reduction process is

In auto-reduction, no external reducing agent is required. In such reduction reaction, the product formed acts as a reducing agent and reduces the oxide to metal. Thus, only reaction II is called auto-reduction. $\begin{aligned} & 2 \mathrm{PbS}+3 \mathrm{O}_2 \xrightarrow{\text { Roasted in air }} 2 \mathrm{PbO}+2 \mathrm{SO}_2 \\ & 2 \mathrm{PbO}+\mathrm{PbS} \longrightarrow 3 \mathrm{~Pb}+\mathrm{SO}_2 \\ & \begin{array}{l}\text { (Act as a } \\ \text { reducing agent) }\end{array}\end{aligned}$