4 Mg0 + KNVO3 + 6 H2O 4 MgII(OH)2 + N-IIIH3 + KOH

This is an oxidation-reduction (redox) reaction:

4 Mg0 - 8 e- 4 MgII (oxidation)

NV + 8 e- N-III (reduction)

Change the oxidation states