Show the oxidation numbers for all atoms in the chemical reactions below. Indicate the pair of

atoms undergoing oxidation and the pair of atoms undergoing reduction. Then identify

oxidizing agent and reducing agent. Some of the reactions are not balanced; you do not need

to balance them!

a$.$ PbO $($s$)+$ CO $($g$)->$ Pb $($s$)+$ CO$2($g$)$

b$.$ K$2$Cr$2$O$7($aq$)+$ HI $($aq$)->$ KI $($aq$)+$ CrI$3($aq$)+$ I$2($s$)+$ H$2$O $($l$)$