Question

Assertion :All the $S$ atoms in $S_4{O}_6^{2-}$ have oxidation number equal to $+2.5$. Reason: Average oxidation number of sulphur in $S_4{O}_6^{2-}$ is $+2.5$.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is D Assertion is incorrect but Reason is correct

Let $x$ be the oxidation number of $S$ in $S_4{O}_6^{-2}$ .
The oxidation number of oxygen is $-2$. The sum of the oxidation numbers is equal to the charge i.e. $-2$.
$4x+6(-2)=-2$ or, $x=-2.5$.
Thus, the average oxidation number of sulfur is $2.5$.
Out of four $S$ atoms, two $S$ atoms are linked to other $S$ atoms only.
These two $S$ atoms have an oxidation number of $0$.
The other two sulphur atoms are linked to $O$ and $S$ atoms. They have oxidation number of $+5$ each.
The structure is given below: