In PbI2, the oxidation number of Pb is +2 and the oxidation number of each I is -1. This can be determined by considering the overall charge of the molecule. Since PbI2 is a neutral molecule, the sum of the oxidation numbers of the atoms in the molecule must be zero. Therefore, the +2 oxidation number of Pb must be balanced by the -2 oxidation number of the two I atoms.