2 KClO4 (s) + 8 Na2SO3 (aq) + H2SO4 (aq) → H2 (g) + 8 Na2SO4 (aq) + K2SO4 (aq) + Cl2 (g)
This is an acid-base reaction (neutralization): Na2SO3 is a base, H2SO4 is an acid.
This is an oxidation-reduction (redox) reaction:
8 SIV - 16 e- → 8 SVI (oxidation)
2 HI + 2 e- → 2 H0 (reduction)
2 ClVII + 14 e- → 2 Cl0 (reduction)
Na2SO3 is a reducing agent, H2SO4 is an oxidizing agent, KClO4 is an oxidizing agent.