4 Fe0 + 10 HNVO3 4 FeII(NVO3)2 + N-IIIH4NVO3 + 3 H2O

This is an oxidation-reduction (redox) reaction:

NV + 8 e- N-III (reduction)

4 Fe0 - 8 e- 4 FeII (oxidation)

Change the oxidation states