A mixture of potassium chlorate, oxalic acid and sulphuric acid is heated. During the reaction which element undergoes maximum change in the oxidation number?

Potassium chlorate (${\text{KClO}}_3$) reacts with oxalic acid (${\text{H}}_2{\text{C}}_2{\text{O}}_4$) in the presence of ${\text{H}}_2{\text{SO}}_4$:Chlorine in ${\text{KClO}}_3$ is in the $+5$ oxidation state. It is reduced to ${\text{Cl}}^{-}$ (in $\text{HCl}$ or chlorides) where its state is $-1$. Change $=|+5-(-1)|=6$.Carbon in oxalic acid (${\text{H}}_2{\text{C}}_2{\text{O}}_4$) is in the $+3$ state. It is oxidized to ${\text{CO}}_2$ ($+4$). Change $=|+3-(+4)|=1$.Sulphur in ${\text{H}}_2{\text{SO}}_4$ ($+6$) remains in $+6$ as sulphate.The element Chlorine ($\text{Cl}$) undergoes the maximum change in oxidation state.