In the reaction, $2\mathrm{Mg}+{\mathrm{O}}_2\to 2\mathrm{MgO}$, _______ is getting oxidised.

Oxidation is defined as-

• Addition of oxygen to a substance, or
• Removal of hydrogen from a substance, or
• Loss of electrons.

• $\underset{\mathrm{Magnesium}}{2\mathrm{Mg}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Magnesium}\mathrm{oxide}}{2\mathrm{MgO}\left(\mathrm{s}\right)}$
• In the given reaction, Magnesium is burning in presence of Oxygen to give Magnesium oxide.
• There is an addition of Oxygen in the reaction, so, Magnesium is getting oxidised here.

Hence, In the reaction, $2\mathrm{Mg}+{\mathrm{O}}_2\to 2\mathrm{MgO}$, Magnesium is getting oxidised.