Question

Oxidation state of $S$ in $H_2{S}_2{O}_8$ is:

• A. 6
• B. 7
• C. 8
• D. 0

Answer 1

The correct option is A 6

The structure of $H_2{S}_2{O}_8$ is given below.
$H-O-\underset{O}{\underset{||}{\stackrel{O}{\stackrel{||}{S}}}}$-O-O-$\underset{O}{\underset{||}{\stackrel{O}{\stackrel{||}{S}}}}$-O-H
In the structure of $H_2{S}_2{O}_8$, two oxygen atoms are involved in peroxide linkage, hence oxidation number will be $-1$ (each). Remaining oxygen atoms will have $-2$ charge. Thus, we can calculate the oxidation state of sulphur ($x$) as follows:
$H_2{S}_2{O}_8=2\underset{H}{(+1)}+2\underset{S}{\left(x\right)}+2\underset{O-O}{(-1)}+6\underset{O}{(-2)}=0$
$x=+6$.