3 Pb0 + 8 HNVO3 3 PbII(NVO3)2 + 2 NIIO + 4 H2O

This is an oxidation-reduction (redox) reaction:

3 Pb0 - 6 e- 3 PbII (oxidation)

2 NV + 6 e- 2 NII (reduction)

Change the oxidation states