2 HNVO3 + 2 FeIISO4 + H2SO4 2 NIVOO + Fe2III(SO4)3 + 2 H2O

This is an oxidation-reduction (redox) reaction:

2 NV + 2 e- 2 NIV (reduction)

2 FeII - 2 e- 2 FeIII (oxidation)

HNO3 is an oxidizing agent, FeSO4 is a reducing agent.