Question

Oxidation number of sulphur in Caros acid $\left(H_{2}S{O}_5\right)$ is:

• A. $+5$
• B. $+8$
• C. $+6$
• D. $+7$

Answer 1

The correct option is C $+6$

In $H_{2}S{O}_5$, one peroxide bond is present.
So, the oxidation number of $2$ oxygen atoms is $-2$. (Compare hydrogen peroxide, $H_2{O}_2$, $2$ atoms of oxygen will get $-1$ oxidation number each).
The remaining $3$ atoms will have $-2$ oxidation number each. This is a special case. Oxidation number of each hydrogen atom is $+1$ only.
So, finally the oxidation number of sulphur is given by,
$x-2-6+2=0$ (equal to zero as the compound is neutral)
or, $x=+6$
The structure of caros acid is as follows: