2 Na3CrIIIO3 + 3 PbIVO2 + 4 NaOH 2 Na2CrVIO4 + 3 Na2PbIIO2 + 2 H2O

This is an oxidation-reduction (redox) reaction:

3 PbIV + 6 e- 3 PbII (reduction)

2 CrIII - 6 e- 2 CrVI (oxidation)

Change the oxidation states