What is the role of an indicator in a titration?

The correct option highlights that the role of an indicator in a titration is to signal the end point of the reaction through a visible color change. Indicators are substances that change color at specific pH levels, allowing the person conducting the titration to visually determine when the reaction between the titrant (the solution being added) and the analyte (the solution being measured) is complete. This color change occurs because the chemical environment of the solution has shifted, indicating that the desired amount of titrant has been added to neutralize the analyte.

In titrations, it's crucial to pinpoint the exact moment when the reaction is complete, and indicators serve as a practical tool for achieving this. They help in visually and accurately establishing when the end point is reached, which corresponds to the stoichiometric point of reaction where the reactants have reacted in their exact proportions.

Other options suggest roles that do not accurately reflect the function of an indicator: increasing pH would not describe the role of an indicator; measuring temperature change is unrelated to an indicator's function; and controlling the flow of the titrant does not pertain to the purpose of an indicator, which is strictly to signal the completion of the titration process through a color change.