2 NH4Cl (aq) + K2Cr2O7 (aq) → N2 (g) + 2 KCl (aq) + Cr2O3 (s) + 4 H2O (l)
This is an oxidation-reduction (redox) reaction:
2 N-III - 6 e- → 2 N0 (oxidation)
2 CrVI + 6 e- → 2 CrIII (reduction)
NH4Cl is a reducing agent, K2Cr2O7 is an oxidizing agent.
This is a precipitation reaction: Cr2O3 is the formed precipitate.
This is a gas evolution reaction, N2 is the formed gas.