2 CoII(OH)2 + 2 NaOH + Cl20 Co2IIIO3H2O + 2 NaCl-I + 2 H2O

This is an oxidation-reduction (redox) reaction:

2 Cl0 + 2 e- 2 Cl-I (reduction)

2 CoII - 2 e- 2 CoIII (oxidation)

Cl2 is an oxidizing agent, Co(OH)2 is a reducing agent.