2 NO2- + 2 H+ + CO(NH2)2 → CO2 + 3 H2O + 2 N2
This is an oxidation-reduction (redox) reaction:
2 N-III - 6 e- → 2 N0 (oxidation)
2 NIII + 6 e- → 2 N0 (reduction)
CO(NH2)2 is a reducing agent, NO2- is an oxidizing agent (synproportionation (comproportionation)).