NH4Cl (aq) + NaNO2 (aq) → N2 (g) + NaCl (aq) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
N-III - 3 e- → N0 (oxidation)
NIII + 3 e- → N0 (reduction)
NH4Cl is a reducing agent, NaNO2 is an oxidizing agent (synproportionation (comproportionation)).
This is a gas evolution reaction, N2 is the formed gas.