Which one of the following statements is not correct?

Sound waves are mechanical longitudinal waves that propagate through media like gases via compressions and rarefactions. In gases, the particles vibrate parallel to the direction of wave travel. The human audible range is typically between 20 Hz and 20,000 Hz. Sound waves with frequencies below 20 Hz are correctly termed 'infrasonic' waves, not ultrasonic [2]. Ultrasonic waves are defined as those with frequencies exceeding the upper limit of human hearing, specifically above 20 kHz. Regarding other properties, the amplitude of a sound wave determines its intensity or loudness; higher amplitudes result in louder sounds. Frequency is perceived as pitch, where higher audible frequencies are described as sharp or high-pitched. Therefore, statement 2 is incorrect because it misidentifies infrasonic waves as ultrasonic.

Sources

1. [1] https://www.sciencedirect.com/topics/physics-and-astronomy/infrasonics
2. [2] https://www.sciencedirect.com/topics/physics-and-astronomy/sound-wave