3 C + 4 K2CrO4 + 10 H2SO4 → 2 Cr2(SO4)3 + 4 K2SO4 + 3 CO2 + 10 H2O
This is an acid-base reaction (neutralization): K2CrO4 is a base, H2SO4 is an acid.
This is an oxidation-reduction (redox) reaction:
3 C0 - 12 e- → 3 CIV (oxidation)
4 CrVI + 12 e- → 4 CrIII (reduction)
C is a reducing agent, K2CrO4 is an oxidizing agent.