Which of the following best illustrates the concept of reaction time?

The concept of reaction time specifically refers to the interval between the presentation of a stimulus and the individual's response to that stimulus. In this context, the "time taken to respond to a sound" is the best illustration of reaction time because it involves an immediate and direct response to auditory stimuli. This aligns with how reaction time is measured in various psychological and physiological studies, where the focus is on how quickly an individual can perceive a stimulus and execute a response.

Other options, while they involve time measurements, do not capture the essence of reaction time as accurately. For instance, the speed of answering a quiz question encompasses cognitive processing time, which includes not only the reaction to a stimulus but also complex thought and decision-making. The duration between taking a test and results being announced reflects a temporal interval unrelated to personal reaction, as it involves a passive waiting period rather than an active response. Similarly, the length of time for verbal communication involves multiple factors beyond just the immediate reaction to a stimulus, such as the encoding and decoding of messages, speech production, and comprehension.