2 NaI (aq) + 3 H2SO4 (aq) + MnO2 (s) → 2 NaHSO4 (aq) + MnSO4 (aq) + I2 (s) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
MnIV + 2 e- → MnII (reduction)
2 I-I - 2 e- → 2 I0 (oxidation)
MnO2 is an oxidizing agent, NaI is a reducing agent.