Ag + 4 HNO2 → AgNO3 + 3 NO + 2 H2O
This is an oxidation-reduction (redox) reaction:
Ag0 - 1 e- → AgI (oxidation)
3 NIII + 3 e- → 3 NII (reduction)
NIII - 2 e- → NV (oxidation)
Ag is a reducing agent, HNO2 is an oxidizing agent, HNO2 is a reducing agent.