5 Fe0 + 12 HNVO3 5 FeII(NVO3)2 + N20 + 6 H2O

This is an oxidation-reduction (redox) reaction:

2 NV + 10 e- 2 N0 (reduction)

5 Fe0 - 10 e- 5 FeII (oxidation)

Change the oxidation states