4 Mg0 + 10 HNVO3 4 MgII(NVO3)2 + N2IO + 5 H2O

This is an oxidation-reduction (redox) reaction:

4 Mg0 - 8 e- 4 MgII (oxidation)

2 NV + 8 e- 2 NI (reduction)

Change the oxidation states