Question

Indicate which of the substance/ion in the following reaction is an oxidising agent and which is a reducing agent?
$2Mg+S{O}_2\to 2MgO+S$.

Answer 1

$2Mg+S{O}_2\to 2MgO+S$.
Oxidising agent- $S{O}_2$. The oxidation number of S decreases from +4 to 0. Thus, S itself is reduced.

Reducing agent- Mg. The oxidation number of Mg increases from 0 to +2. Thus, Mg itself is oxidised.

Note: Gain of oxygen is oxidation. Thus, $Mg$ is oxidised to $MgO$.

Any species that is oxidised acts as reducing agent.

Any species that is reduced acts as oxidising agent.