Which half-reaction is most easily oxidized?

Which half-reaction is most easily oxidized?

Answer options:

a. Al3+ + 3e- Al = -1.66 V
b. Cu2+ + 2e- Cu = 0.34 V
c. Fe3+ + e- Fe2+ = 0.77 V
d. Na+ + e- Na = -2.71 V
e. Pb2+ + 2e- Pb = -0.13 V