In which of the following reactions, chlorine acts as an oxidizing agent ?
$\mathrm{I}:{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}+{\mathrm{Cl}}_2⟶{\mathrm{CH}}_3\mathrm{CHO}+2\mathrm{HCl}$
$\mathrm{II}:{\mathrm{CH}}_3\mathrm{CHO}+{\mathrm{Cl}}_2⟶{\mathrm{CCl}}_3\mathrm{CHO}+\mathrm{HCl}$
$\mathrm{III}:{\mathrm{CH}}_4+{\mathrm{Cl}}_2\stackrel{\text{ hv }}{⟶}{\mathrm{CH}}_3\mathrm{Cl}+\mathrm{HCl}$
The correct answer is :