3 HgS-II + 2 HNVO3 + 6 HCl 3 HgCl2 + 3 S0 + 2 NIIO + 4 H2O

This is an oxidation-reduction (redox) reaction:

3 S-II - 6 e- 3 S0 (oxidation)

2 NV + 6 e- 2 NII (reduction)

Change the oxidation states