Final answer:
Frequency is the number of oscillations per unit time and is measured in hertz (Hz). It is associated with the perception of pitch in sound.
Step-by-step explanation:
Frequency is the number of oscillations per unit time. It is measured in hertz (Hz), which is defined as the number of oscillations per second. Frequency is also associated with the perception of pitch in sound. For example, high-frequency sounds have a higher pitch, while low-frequency sounds have a lower pitch. Therefore, the correct answer to the question is B) hertz.