When a magnesium ribbon burns in air with a dazzling flame and forms white ash, is magnesium oxidised or reduced? Why?

In the reaction represented by the equation:

${\mathrm{MnO}}_2+4\mathrm{HCl}\to {\mathrm{MnCl}}_2+2{\mathrm{H}}_2\mathrm{O}+{\mathrm{Cl}}_2$
(i) name the substance oxidised.
(ii) name the oxidising agent.
(iii) name the substance reduced.
(iv) name the reducing agent.

Give an example of an oxidation reaction.