Arrange the average oxidation number of sulfur in increasing order: P $\mathrm{Na}{}_2\mathrm{S}{}_2\mathrm{O}{}_3$ (sodium thiosulfate), Q $\mathrm{Na}{}_2\mathrm{S}{}_4\mathrm{O}{}_6$ (sodium tetrathionate), R $\mathrm{Na}{}_2\mathrm{S}{}_2\mathrm{O}{}_4$ (sodium dithionite), S $\mathrm{Na}{}_2\mathrm{SO}{}_3$ (sodium sulfite).

1. A$\mathrm{P}<\mathrm{Q}<\mathrm{R}<\mathrm{S}$
2. B$\mathrm{Q}<\mathrm{P}<\mathrm{R}<\mathrm{S}$
3. C$\mathrm{P}<\mathrm{R}<\mathrm{Q}<\mathrm{S}$
4. D$\mathrm{S}<\mathrm{R}<\mathrm{Q}<\mathrm{P}$