Question

What is the oxidation number of $Mn$ in $KMn{O}_4$ and of $S$ in $N{a}_2{S}_2{O}_3$ ?

• A. $+7,-2$
• B. $+5,-2$
• C. $+7,+2$
• D. $+5,+2$

Answer 1

The correct option is C $+7,+2$

Let, the oxidation number of $Mnbex$.
We know that, oxidation number of $K=+1$
Oxidation number of $O=-2$
Oxidation number of $K=+1$
$\therefore +1+x+4(-2)=0$
$\Rightarrow +1+x-8=0$
$\Rightarrow x=+8-1=+7$
Hence, oxidation number of $Mn$ in $KMn{O}_4$ is $+7$.
Similarly, for $S$ in $N{a}_2{S}_2{O}_3$,
$2\left(OxidationnumberofNa\right)+2\left(OxidationnumberofS\right)+3\left(OxidationnumberofO\right)=0$
$2\times (+1)+2x+3(-2)=0$
$x=+2$
Hence, Oxidation number of $S$ in $N{a}_2{S}_2{O}_3=+2$