Question

A solution of sulphur dioxide in water reacts with $H_{2}S$ precipitating sulphur. Here sulphur dioxide acts as

• A. an oxidising agent
• B. a reducing agent
• C. an acid
• D. a catalyst

Answer 1

The correct option is A an oxidising agent

First - let us write down the reaction:
$S{O}_2+2H_{2}S⟶3S+2H_{2}O$
In $H_{2}S$, sulphur has an oxidation number of -2. In $S{O}_2$ Sulphur has an oxidation number of +4.
On the right-hand side, we only have elemental sulphur whose oxidation number is 0. The sulphur in $S{O}_2$ changes its oxidation number from +4 to 0.
This means that the sulphur is gaining electrons. We know that when a reactant gains electrons, it gets reduced. Hence, $S{O}_2$ is getting reduced.
Also, the reactant that gets reduced is the oxidising agent. Hence, here, $S{O}_2$ acts as an oxidising agent.