For the reaction ${\mathrm{Fe}}_2{\mathrm{O}}_3+3\mathrm{CO}\to 2\mathrm{Fe}+3{\mathrm{CO}}_2$, the volume of carbon monoxide required to reduce one mole of ferric oxide is

Based on the given equation, it is clear that 1 mole of Fe₂​O_3​ i.e. ferric oxide is reduced by  3 carbon monoxides.

1 mole of any compound occupies 22.4 l of volume. 

So, the volume of carbon monoxide required to reduce one mole of ferric oxide is = 3 × 22.4 dm³=67.2 dm³.