Question

Which substance/ion is oxidised and which substance/ion is reduced in the following reaction?
$2I^{-}+C{l}_2\to 2C{l}^{-}+I_2$.

Answer 1

$2I^{-}+C{l}_2\to 2C{l}^{-}+I_2$.
Oxidised- $I^{-}$ The oxidation number of I increases from -1 to 0. Thus, I itself is oxidised and acts as reducing agent.
Reduced- $C{l}_2$. The oxidation number of Cl decreases from 0 to -1. Thus, Cl itself is reduced and acts as oxidising agent.

Note:
Any species that is oxidised acts as reducing agent.
Any species that is reduced acts as oxidising agent.