Question

The average oxidation states of sulphur in $N{a}_2{S}_2{O}_3$ and $N{a}_2{S}_4{O}_6$ are, respectively :

• A. $+5$ and $+2$
• B. $+2$ and $+2.5$
• C. $+5$ and $2.5$
• D. $+2$ and $+4$

Answer 1

The correct option is B $+2$ and $+2.5$

Let $x$ be the oxidation number of sulphur in $N{a}_2{S}_2{O}_3$.
For a neutral compound, sum of oxidation states of all elements must be zero.
$2+2x+3(-2)=0$
$2x=6-2$
$2x=4$
$x=+2$
Suppose $y$ be the oxidation number of sulphur in $N{a}_2{S}_4{O}_6$.
$2+4y+3(-2)=0$
$4y=12-2$
$4y=10$
$y=+2.5$
The average oxidation states of sulphur in $N{a}_2{S}_2{O}_3$ and $N{a}_2{S}_4{O}_6$ are respectively $+2$ and $+2.5$.