3 HClVIIO4 + 8 NIIO + 4 H2O 8 HNVO3 + 3 HCl-I

This is an oxidation-reduction (redox) reaction:

3 ClVII + 24 e- 3 Cl-I (reduction)

8 NII - 24 e- 8 NV (oxidation)

HClO4 is an oxidizing agent, NO is a reducing agent.