4 NaCl (aq) + 2 H2SO4 (aq) + MnO2 (s) → Cl2 (g) + MnCl2 (aq) + 2 Na2SO4 (aq) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
MnIV + 2 e- → MnII (reduction)
2 Cl-I - 2 e- → 2 Cl0 (oxidation)
MnO2 is an oxidizing agent, NaCl is a reducing agent.