2 NaNO2 + 2 BaI2 + 2 H2SO4 → Ba2SO4 + Na2SO4 + 2 I2 + 2 NO + 2 H2O
This is an oxidation-reduction (redox) reaction:
SVI + 2 e- → SIV (reduction)
4 I-I - 4 e- → 4 I0 (oxidation)
2 NIII + 2 e- → 2 NII (reduction)
H2SO4 is an oxidizing agent, BaI2 is a reducing agent, NaNO2 is an oxidizing agent.