Six moles of $\mathrm{PbS}$ are roasted so that exactly half is converted to $\mathrm{PbSO}{}_4$ ($\mathrm{PbS}+2\mathrm{O}{}_2\to \mathrm{PbSO}{}_4$) and the rest is left unchanged. Air is then cut off and the mixture heated: $\mathrm{PbS}+\mathrm{PbSO}{}_4\to 2\mathrm{Pb}+2\mathrm{SO}{}_2$. The volume of $\mathrm{O}{}_2$ (STP) used in the first stage and the mass of lead finally obtained (Pb = 207) are

1. A$67.2\mathrm{L}$ and $1242\mathrm{g}$
2. B$268.8\mathrm{L}$ and $1242\mathrm{g}$
3. C$134.4\mathrm{L}$ and $1242\mathrm{g}$
4. D$134.4\mathrm{L}$ and $621\mathrm{g}$