Acidified $ \text{KMn}{{\text{O}}_{\text{4}}} $ oxidises oxalic acid to $ \text{C}{{\text{O}}_{2}}. $ What is the volume (in litres) of $ {{10}^{-4}}\text{M}\,\text{KMn}{{\text{O}}_{\text{4}}} $ required to completely oxidise 0.5 L of $ {{10}^{-2}}\text{M} $ oxalic acid in acid medium?