How does a salt bridge provide an electrical connection between the two electrodes?

A salt bridge is an essential component in electrochemical cells, serving to complete the circuit between the two half-cells while maintaining electrical neutrality. It contains an electrolyte solution, typically composed of inert salts, which dissociates into ions. This setup allows the ions in the salt bridge to migrate between the two half-cells.

As chemical reactions occur at the electrodes, one electrode generates positive ions (cations) while the other generates negative ions (anions). This leads to a build-up of charge in each half-cell, which would eventually stop the flow of electrons if not balanced. The salt bridge facilitates the movement of ions; cations flow toward the cathode (the electrode where reduction occurs) to neutralize the excess negative charge, while anions flow toward the anode (the electrode where oxidation occurs) to counterbalance the positive charge buildup. This movement of ions is crucial for maintaining the overall charge balance in the electrochemical cell and allows for continuous electron flow through the external circuit.

In contrast, the other options do not align with the function of the salt bridge. Specifically, electrons do not flow directly through the bridge; they travel through the external circuit. Heat conduction is not a role of the salt bridge in terms of its primary purpose