# How would you determine the oxidation number for sodium sulfate?

Oxygen assumes its usual oxidation state of $- I I$. Therefore, $S$ here has its maximum oxidation number of $V {I}^{+}$.
Sum up the oxidation numbers: $4 \times \left(- I I\right) + {S}_{O N} = {2}^{-}$, the charge on anion. Therefore, S_(ON) = ?? How would you determine the oxidation numbers of the sulfurs in thiosulfate anion, ${S}_{2} {O}_{3}^{2 -}$?