We’re being asked to determine which among half-cell reactions that lead to the largest positive cell emf.
When a balanced reaction is given, identify the anode and the cathode half-reactions by determining the changes in oxidation states of each species based on the given reaction:
Given the following half-reactions and associated standard reduction potentials:
AuBr4-(aq) + 3e- → Au(s) + 4Br-(aq)
Eredo= - 0.858V
Eu3+(aq) + e- → Eu2+(aq)
Eredo= - 0.43V
IO-(aq) + H2O(l) + 2e- → I-(aq) + 2OH-(aq)
Eredo= + 0.49V
Sn2+(aq) + 2e- → Sn(s)
Eredo= - 0.14V
Write the cell reaction for the combination of these half-cell reactions that leads to the largest positive cell emf.