6 K3Fe(CN)6 (aq) + Cr2O3 (s) + 10 KOH (aq) → 6 K4Fe(CN)6 (aq) + 2 K2CrO4 (aq) + 5 H2O (l)
This is an oxidation-reduction (redox) reaction:
6 FeIII + 6 e- → 6 FeII (reduction)
2 CrIII - 6 e- → 2 CrVI (oxidation)
K3Fe(CN)6 is an oxidizing agent, Cr2O3 is a reducing agent.