Question:
In mildly alkaline medium, thiosulphate ion is oxidized by $\mathrm{MnO}_{4}^{-}$to "A". The oxidation state of sulphur in "A" is_______.
Solution:
$\mathrm{MnO}_{4}^{-}+\mathrm{S}_{2} \mathrm{O}_{3}^{2-} \rightarrow \mathrm{MnO}_{2}+\underset{(\mathrm{A})}{\mathrm{SO}_{4}^{2-}}$
Oxidation state of ' $\mathrm{S}$ ' in $\mathrm{SO}_{4}{ }^{2-}$
$=+6$