Question

What is the oxidation number of sulphur in $H_2{S}_2{O}_8$?

• A. 7
• B. 5
• C. 6
• D. This compound does not exist

Answer 1

The correct option is C 6

$H_2{S}_2{O}_8+2H_{2}O⟶2H_2{SO}_4+H_2{O}_2$
The structure of $H_2{S}_2{O}_8$ has been given below:
We can see that it has a peroxide linkage in which each oxygen atom has oxidation number of $-1$.
Let $x$ be the oxidation state of S in $H_2{S}_2{O}_8$.
Since the overall charge on the complex is $0$, the sum of oxidation states of all elements in it should be equal to $0$.
Therefore, $+2+2x-2\left(4\right)-2-4=0$
or, $x=+6$