Chemistry - Redox Reactions Question with Solution | TestHub

The given reaction is $3{\text{H}}_3{\text{AsO}}_{3(aq)}+{\text{BrO}}_{3(aq)}^{-}⟶{\text{Br}}_{(aq)}^{-}+3{\text{H}}_3{\text{AsO}}_{4(aq)}$

Let the oxidation state of As in ${\text{H}}_3{\text{AsO}}_3$ be $x$.
$3(+1)+x+3(-2)=0\Rightarrow x=+3$

Let the oxidation state of Br in ${\text{BrO}}_3^{-}$ be $y$.
$y+3(-2)=-1\Rightarrow y=+5$

Let the oxidation state of As in ${\text{H}}_3{\text{AsO}}_4$ be $z$.
$3(+1)+z+4(-2)=0\Rightarrow z=+5$

The oxidation state of Br in ${\text{Br}}^{-}$ is $-1$.

The oxidation state of As increases from $+3$ to $+5$, so ${\text{H}}_3{\text{AsO}}_3$ undergoes oxidation and acts as a reducing agent.

The oxidation state of Br decreases from $+5$ to $-1$, so ${\text{BrO}}_3^{-}$ undergoes reduction and acts as an oxidising agent.

The change in oxidation state of the oxidising agent is $+5$ to $-1$.

Answer: $+5\text{to}-1$