Copper is extracted from $45.9\mathrm{kg}$ of an ore containing $80.0\%$ $\mathrm{CuFeS}{}_2$ by mass. Smelting follows $2\mathrm{CuFeS}{}_2+\mathrm{O}{}_2\to \mathrm{Cu}{}_2\mathrm{S}+2\mathrm{FeS}+\mathrm{SO}{}_2$ and $2\mathrm{FeS}+3\mathrm{O}{}_2\to 2\mathrm{FeO}+2\mathrm{SO}{}_2$, and the iron(II) oxide is removed as slag by $\mathrm{FeO}+\mathrm{SiO}{}_2\to \mathrm{FeSiO}{}_3$. Taking $\mathrm{Cu}=63.5$, $\mathrm{Fe}=56$, $\mathrm{S}=32$, $\mathrm{Si}=28$, $\mathrm{O}=16$, and assuming all the iron goes to slag and all the copper to $\mathrm{Cu}{}_2\mathrm{S}$, the mass of silica needed and the mass of $\mathrm{Cu}{}_2\mathrm{S}$ obtained are

1. A12.0 kg and 31.8 kg
2. B6.0 kg and 15.9 kg
3. C24.0 kg and 15.9 kg
4. D12.0 kg and 15.9 kg