3 Na2SO3 (aq) + 2 KMnO4 (aq) + H2O (l) → 2 Na2SO4 (aq) + 2 MnO2 (s) + 2 NaOH (aq) + K2SO4 (aq)
This is an oxidation-reduction (redox) reaction:
2 MnVII + 6 e- → 2 MnIV (reduction)
3 SIV - 6 e- → 3 SVI (oxidation)
KMnO4 is an oxidizing agent, Na2SO3 is a reducing agent.