Question

Which half-reaction is most easily oxidized?

Answer 1

Hint: What does the positive or negative sign on the voltage indicate?

Answer 2

Alright then!
To introduce the basis, I want to believe that you know that reduction is the gain of electrons and oxidation is the loss of electrons.
Next, you should know that of a half equation has a positive potential difference, it is of an oxidation character, because, related from before, as the atom loses electrons, it gets in excess of positive charges.
The opposite pf this is true: if it is negative potential difference, it is of a reduction character...
Furthermore, the more positive the potential difference, the more the equation is likely to be oxidised.
Therefore, according to your question,

Answer 3

According to your question, the third alternative is the most positive, being the required answer. I hope I am correct.

Answer 4

Wait, isnt it giving you standard reduction potentials? That would mean the greater the potential, the greater the chance of reduction. You therefore want the most negative reduction potential, so the most negative would be the most likely to lose electrons. Most negative is what i would go with. Another way to think of this would be "What would lose electrons the easiest?" or "What would want to give away its electrons the most?". The answers to those questions can be answered quite easily. Alkali metals and alkaline earth metals love to oxidize and have an octet isoelectronic with the previous noble gas!