Ultrasound waves are a type of sound waves that have a frequency higher than the upper limit of human hearing, which is typically around 20,000 Hz.

Option 1 states that ultrasound waves have a higher speed compared to audible sound waves. However, the speed of sound in a particular medium depends on the properties of that medium, such as temperature, composition, and density. It is not specifically related to the frequency of the wave. Therefore, option 1 is incorrect.

Option 2 states that ultrasound waves have a higher frequency compared to audible sound waves. This is true. Ultrasound waves have frequencies greater than 20,000 Hz, while audible sound waves have frequencies between 20 Hz and 20,000 Hz. The higher frequency of ultrasound waves allows them to be used in various applications such as medical imaging, industrial testing, and underwater communication.

Option 3 states that ultrasound waves have a longer wavelength compared to audible sound waves. Wavelength is inversely proportional to frequency, so higher frequency waves have shorter wavelengths. Therefore, option 3 is incorrect.

Option 4 states that ultrasound waves have both a higher speed and frequency compared to audible sound waves. This is the correct answer. Although the speed of sound is not affected by frequency, the combination of