Answer:
Option b) a potential difference between the indicator and reference electrode under equilibrium conditions.
Step-by-step explanation:
Potentiometric method is often used to find the concentration of a solute in solution.
In potentiometric measurements, the potential between 2 electrodes is measured employing a high electric resistance meter.
Use of a high electric resistance meter in vital, because it ensures that current flow is negligible. Since there's no flowing current, there will be no chemical reactions, therefore the system is in equilibrium.