Which method involves making multiple measurements during the reaction at specific time intervals?

The kinetic method is used to monitor a reaction continuously or at specific time intervals to observe how the concentration of a reactant or product changes over time. By making multiple measurements during the progression of a reaction, the kinetic method allows for the determination of reaction rates and provides a detailed understanding of the dynamics of the reaction.

In contrast, the fixed-time method measures the concentration at a predetermined endpoint or time limit, which does not account for changes occurring throughout the reaction. The endpoint method, similar to the fixed-time method, focuses on the value at a single final point rather than the changes occurring over the course of the reaction, therefore lacking the detailed time-based data afforded by the kinetic method. Lastly, the qualitative method is primarily concerned with identifying the presence or absence of substances rather than measuring concentration changes over time.

Therefore, the kinetic method is correctly identified as the approach that incorporates multiple measurements over time, enabling a comprehensive analysis of the reaction dynamics.