6 FeIISO4 + 2 HNVO3 + 3 H2SO4 3 Fe2III(SO4)3 + 2 NIIO + 4 H2O

This is an oxidation-reduction (redox) reaction:

2 NV + 6 e- 2 NII (reduction)

6 FeII - 6 e- 6 FeIII (oxidation)

Change the oxidation states