The sum of the oxidation states of sulphur atoms in ${\mathrm{H}}_2{\mathrm{ }\mathrm{S}}_2{\mathrm{O}}_5\text{ is }$................

The oxidation state of oxygen is -2. The oxidation state of hydrogen is +1 .

Oxidation state of sulphur can be calculated as follows:

$$\begin{gathered} 2(\mathrm{oxidation} \mathrm{state} \mathrm{of} \mathrm{S})+5(\mathrm{oxidation} \mathrm{state} \mathrm{of} \mathrm{O})+2(\mathrm{oxidation} \mathrm{state} \mathrm{of} \mathrm{H})=0 \\ 2(\mathrm{oxidation} \mathrm{state} \mathrm{of} \mathrm{S})+5(-2)+2(+1)=0 \\ \mathrm{oxidation} \mathrm{state} \mathrm{of} \mathrm{S}=+5 \end{gathered}$$

So, oxidation state of sulphur is +4 . But there are two sulphur atoms hence, the sum of total S atoms in H₂S₂O₅ is 8.