Chapter 19, Problem 16QP

Which species in each pair is a better oxidizing agent under standard-state conditions: ${\text{(a) Br}}_{\text{2}}{\text{ or Au}}^{\text{3+}}{\text{, (b) H}}_{\text{2}}{\text{ or Ag}}^{\text{+}}{\text{, (c) Cd}}^{\text{2+}}{\text{ or Cr}}^{\text{3+}},{\text{ (d) O}}_{\text{2}}$ in acidic media or ${\text{O}}_{\text{2}}$ in basic media?