$25.0\mathrm{mL}$ of $0.100\mathrm{M}$ $\mathrm{Na}{}_2\mathrm{S}{}_2\mathrm{O}{}_3$ needs $25.0\mathrm{mL}$ of $0.0500\mathrm{M}$ iodine solution ($\mathrm{S}{}_2\mathrm{O}{}_3{}^{2-}$ goes to $\mathrm{S}{}_4\mathrm{O}{}_6{}^{2-}$). If the same amount of thiosulphate is instead oxidised completely to sulphate ($\mathrm{S}{}_2\mathrm{O}{}_3{}^{2-}+4\mathrm{Cl}{}_2+5\mathrm{H}{}_2\mathrm{O}\to 2\mathrm{SO}{}_4{}^{2-}+8\mathrm{Cl}{}^{-}+10\mathrm{H}{}^{+}$) by $0.0500\mathrm{M}$ $\mathrm{Cl}{}_2$ water, the volume of chlorine water needed is

1. A50 mL
2. B400 mL
3. C25 mL
4. D200 mL