Identify the oxidizing agent and reducing agent in the given reaction, by looking at the gain and loss of oxygen : 

$2{\mathrm{Mg}}_{\left(\mathrm{s}\right)}+{\mathrm{O}}_{2\left(\mathrm{g}\right)} \to 2{\mathrm{MgO}}_{\left(\mathrm{s}\right)}$

Identify the oxidising agent and reducing agent in the given reaction, by looking at the gain and loss of oxygen.

${\mathrm{Fe}}_2{\mathrm{O}}_{3\left(\mathrm{s}\right)}+3{\mathrm{CO}}_{\left(\mathrm{g}\right)} \to 2{\mathrm{Fe}}_{\left(\mathrm{l}\right)}+3{\mathrm{CO}}_{2\left(\mathrm{g}\right)}$

Identify the oxidising and reducing agent in the following reaction : 

$2\mathrm{Fe}+3{\mathrm{Cl}}_2 \to 2{\mathrm{FeCl}}_3$

Identify the oxidizing and reducing agent in the following reaction :

$\mathrm{Fe}+{\mathrm{CuSO}}_4 \to {\mathrm{FeSO}}_4+\mathrm{Cu}$