Which of the following correctly defines acoustic frequency?

Acoustic frequency is defined as the number of cycles of a wave that occur in one second, which directly relates to how quickly the waves oscillate. This frequency is typically expressed in hertz (Hz), where one hertz corresponds to one cycle per second. Understanding acoustic frequency is critical in sonography, as it influences the resolution and penetration of ultrasound waves; higher frequencies provide better resolution but less penetration, while lower frequencies allow deeper tissue penetration with less detail.

The other options address different attributes of waves but do not accurately define frequency itself. For example, the length of one cycle pertains to wavelength, the number of pulses in a cycle does not have a standard definition in wave mechanics, and the strength of the compression wave refers to amplitude rather than frequency. Therefore, option C accurately captures the definition of acoustic frequency.