2 NaClO2 (aq) + Cl2 (g) → 2 ClO2 (g) + 2 NaCl (aq)
This is an oxidation-reduction (redox) reaction:
2 Cl0 + 2 e- → 2 Cl-I (reduction)
2 Cl0 - 8 e- → 2 ClIV (oxidation)
2 ClIII + 8 e- → 2 Cl-I (reduction)
2 ClIII - 2 e- → 2 ClIV (oxidation)
Cl2 is an oxidizing agent, Cl2 is a reducing agent, NaClO2 is an oxidizing agent, NaClO2 is a reducing agent.