Natural rubber (repeat unit $\mathrm{C}{}_5\mathrm{H}{}_8$, 68 g/mol, one $\mathrm{C}=\mathrm{C}$ per unit) adds bromine across its double bonds, $\mathrm{C}=\mathrm{C}+\mathrm{Br}{}_2\to \mathrm{CBr}-\mathrm{CBr}$. In a vulcanised sample, 4 percent of the isoprene units have lost their $\mathrm{C}=\mathrm{C}$ in forming sulfur links. Ignoring the mass of sulfur, 136 g of the polyisoprene part of this sample takes up how many moles of $\mathrm{Br}{}_2$ (assuming all remaining double bonds react)?

1. A2.00 mol
2. B0.08 mol
3. C1.92 mol
4. D1.96 mol