2 KClO3 (aq) + H2C2O4 (aq) + 2 H2SO4 (aq) → 2 ClO2 (g) + 2 CO2 (g) + 2 KHSO4 (aq) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
2 CIII - 2 e- → 2 CIV (oxidation)
2 ClV + 2 e- → 2 ClIV (reduction)
H2C2O4 is a reducing agent, KClO3 is an oxidizing agent.
This is a gas evolution reaction, ClO2 and CO2 is the formed gas.