PbO2 (s) + 2 KBr (aq) + 2 H2SO4 (aq) → Br2 (aq) + PbSO4 (s) + K2SO4 (aq) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
2 Br-I - 2 e- → 2 Br0 (oxidation)
PbIV + 2 e- → PbII (reduction)
KBr is a reducing agent, PbO2 is an oxidizing agent.