2025 MCAT Practice Exam – Complete Prep Resource

The correct answer reflects the fundamental role of salt bridges in galvanic cells, which is to prevent charge build-up in the half-cells. In a galvanic cell, oxidation occurs at the anode and reduction at the cathode, leading to the generation of free electrons and the movement of ions. As electrons flow from the anode to the cathode through the external circuit, positive ions accumulate at the anode and negative ions at the cathode, which would ultimately halt the flow of electrons due to charge imbalance.

The salt bridge, typically filled with an electrolyte solution, maintains electrical neutrality in the half-cells by allowing ions to flow between them. This ion migration combats charge buildup by neutralizing the positive charge at the anode and the negative charge at the cathode, therefore allowing the redox reactions to continue uninterrupted.

While the other options may make sense in different contexts, they do not accurately describe the function of the salt bridge in galvanic cells. The salt bridge does not enhance electrical conductivity in the electrolyte as a primary function, nor does it serve as a barrier to ion migration or provide structural stability to any membrane. Its primary purpose is to facilitate ion exchange and maintain charge balance, thus ensuring the continuous operation of the cell.