Which of the following balances the oxidation half reaction: Zn(s) → Zn2+(aq) 1. 2Zn(s) → Zn2+(aq) 2. 2Zn(s?

I would say number 3. This is because the primary concern in this half reaction is to balance the charges. The left hand side has a charge of 0 because there is only solid Zn. the other side as written is at 2+, so it needs a 2- somewhere to bring it to 0. This is done by adding 2e- to the right side of the equation making your half reaction Zn(s) --> Zn2+(aq) + 2e-