What is the most likely respiratory rate of an adult with tachypnea?

Tachypnea refers to an abnormally rapid breathing rate, which is typically defined as an adult respiratory rate exceeding 20 breaths per minute. In the context of the choices provided, a respiratory rate of 20 breaths per minute is at the threshold for tachypnea, whereas a rate of 24 breaths per minute is considered distinctly tachypneic.

In assessing the options, while a rate of 12 breaths per minute is considered normal for adults, 16 breaths per minute is also within the normal range. Thus, neither of these rates would indicate tachypnea. A rate of 20 breaths per minute reflects the onset of tachypnea, indicating that the individual is likely experiencing respiratory distress or an increased metabolic demand. Given these considerations, the correct answer reflects the common clinical understanding of respiratory rates associated with tachypnea, which supports the reasoning behind the selection of that specific rate.