8 NaI + 2 Na2CrO4 + 8 H2SO4 → Cr2(SO4)2 + 6 Na2SO4 + 4 I2 + 8 H2O
This is an acid-base reaction (neutralization): Na2CrO4 is a base, H2SO4 is an acid.
This is an oxidation-reduction (redox) reaction:
2 SVI + 8 e- → 2 SII (reduction)
8 I-I - 8 e- → 8 I0 (oxidation)
H2SO4 is an oxidizing agent, NaI is a reducing agent.