Which of the following waves is used in sonography?

The figure represents the instantaneous picture of a longitudinal harmonic wave travelling along the negative $x$-axis. Identify the correct statement$(s)$ related to the movement of the points shown in the figure. The points of maximum rarefaction are

Which of the following frequencies of sound waves is audible to human beings?

Sound waves are not transmitted over long distances because:

$SONAR$ emits which of the following waves?

Find the wavelength of a sound wave of frequency $4.2 \text{ MHz}$ travelling with a speed of $1.7 \text{ km/s}$.