Ag2S-II + 4 HNVO3 2 AgNVO3 + 2 NIVO2 + S0 + 2 H2O

This is an oxidation-reduction (redox) reaction:

S-II - 2 e- S0 (oxidation)

2 NV + 2 e- 2 NIV (reduction)

Change the oxidation states