Cr2SO4 + 16 NaOH + 5 Cl2 → Na2SO4 + 2 Na2CrO4 + 10 NaCl + 8 H2O
This is an oxidation-reduction (redox) reaction:
SII - 4 e- → SVI (oxidation)
10 Cl0 + 10 e- → 10 Cl-I (reduction)
2 CrIII - 6 e- → 2 CrVI (oxidation)
Cr2SO4 is a reducing agent, Cl2 is an oxidizing agent, Cr2SO4 is a reducing agent.