What is the primary function of an indicator in a titration?

An indicator in a titration serves the primary function of signaling the endpoint of the titration process. As a titration progresses, the solution being analyzed will undergo a color change at a specific pH level or at the point where the reactants have completely reacted with each other. This color change provides a visual cue to the analyst that the endpoint has been reached, allowing for accurate determination of the concentration of the unknown solution.

The use of indicators is critical because they provide an easy and immediate visual indication of when the amount of titrant added is stoichiometrically equivalent to the amount of analyte in the solution. This contrasts with simply measuring pH or increasing reactant concentration, which do not directly provide the information needed to identify the endpoint during a titration. Thus, the primary role of the indicator is to communicate the completed reaction, making option C the correct choice.