What is the phase difference between the displacement wave and the pressure wave in a sound wave?

For a particular sound wave propagating in air, a path difference between two points is $0.54 \, m$ which is equivalent to a phase difference of $(1.8 \pi)$. If the velocity of the sound wave in air is $330 \, m/s$, the frequency of this wave is: (in $Hz$.)

What is the effect of humidity on sound waves when humidity increases?

$A$ hospital uses an ultrasonic scanner to locate tumours in a tissue. What is the wavelength of sound in the tissue in which the speed of sound is $1.7 \; km/s$? The operating frequency of the scanner is $4.2 \; MHz$.

Earthquakes generate sound waves inside the earth. Unlike a gas,the earth can experience both transverse $(S)$ and longitudinal $(P)$ sound waves. Typically,the speed of $S$ wave is about $4.0 \; km/s$,and that of $P$ wave is $8.0 \; km/s$. $A$ seismograph records $P$ and $S$ waves from an earthquake. The first $P$ wave arrives $4 \; min$ before the first $S$ wave. Assuming the waves travel in a straight line,at what distance (in $km$) does the earthquake occur?

$A$ wave with a wavelength of $0.60 \ cm$ is produced in air and it travels at a speed of $300 \ ms^{-1}$. This wave is classified as: