Question

The oxidation states of sulphur in $S_2{O}_4^{2-}$ is :

Answer 1

Let $x$ be the oxidation state of $S$ in $S_2{O}_4^{2-}$.
Since the overall charge on the complex is $-2$, the sum of oxidation states of all elements in it should be equal to $-2$.
Therefore, $2x+4(-2)=-2$
or, $x=+3$