Question

The oxidation number of sulphur in $H_2{S}_2{O}_8$ is:

• A. $+2$
• B. $+4$
• C. $+6$
• D. $+7$

Answer 1

The correct option is C $+6$

$H-O-\stackrel{\stackrel{O}{||}}{\underset{\underset{O}{||}}{S}}-O-O-\stackrel{\stackrel{O}{||}}{\underset{\underset{O}{||}}{S}}-O-H$

$\because$ $2O$-atoms are in peroxide linkage
$\therefore$ Their oxidation state$=-1$
and, oxidation state of remaining $6O$-atoms $=-2$
Oxidation state of $H-$ atoms $=+1$

Let oxidation state of $S$ atom $=x$
$S_2$ $H_2$ $O_6$ $O_2$

$\therefore 2x+2(+1)+6(-2)+2(-1)=0$

$2x+2-12-2=0$

$\therefore x=+6$.