Why dilute H2SO4 is added to oxali acid solution in redox reaction

To prevent the hydrolysis and to catalyse the reaction.

Explanation:

Sulphuric acid is the catalyst and also a dehydrating agent in this reaction. Sulphuric acid is using in redox reaction because sulphuric acid is providing H + ions which is necessary for this reaction to occur more quickly, but the sulphate ions from the sulphuric acid barely react during this process. So H2SO4 is adding in this reaction to make it more acidic. H2SO4 is preventing hydrolysis by providing excess H + ions into the reaction. H2SO4 is stable towards the direction of oxidation.