6 NaOH (aq) + 3 Cl2 (g) → NaClO3 (aq) + 5 NaCl (aq) + 3 H2O (l)
This is an oxidation-reduction (redox) reaction:
5 Cl0 + 5 e- → 5 Cl-I (reduction)
Cl0 - 5 e- → ClV (oxidation)
Cl2 is both an oxidizing and a reducing agent (disproportionation (dismutation)).