Question

Indicate which of the substance/ion in the following reaction is an oxidising agent and which is a reducing agent?
$2I^{-}+H_2{O}_2\to 2O{H}^{-}+I_2$.

Answer 1

$2I^{-}+H_2{O}_2\to 2O{H}^{-}+I_2$.
Oxidising agent- $H_2{O}_2$ The oxidation number of O decreases from -1 to -2. Thus, O itself is reduced.
Reducing agent- $I^{-}$. The oxidation number of I increases from -1 to 0. Thus, I itself is oxidised.

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