What is the function of a salt bridge in a galvanic cell?

Question

1. To permit electrons to flow through the solution.
2. To maintain a steady flow of reactants from the cathode to the anode.
3. To form complex ions with the products of oxidation at the anode.
4. To maintain electrical neutrality in the cell.
5. To act as a catalyst.

Would 4 be the answer because the wire permits the flow or would it be 2 because it keeps the flow steady?

Answer 1

No, I think your first answer is the one.
Look at it this way. Draw a cell with a salt bridge between. Make it Zn metal dipping into Zn(NO3)2 solution on the left and Cu metal dipping into Cu(NO3)2 solution on the right. When the reaction starts, Zn goes to Zn^2+ + 2e on the left. On right Cu2+ ions go to Cu metal. So on the left the Zn^2+ ions need NO3^- to hook up with and on the right the Cu^2+ are being removed which leaves an excess of NO3^-. So the excess of nitrate on the right can migrate through the salt bridge and go over to the Zn cell and hook up with those extra Zn^2+ being produced.