The following phenomenon cannot be observed for sound waves:

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

$A$ man,standing between two cliffs,claps his hands and starts hearing a series of echoes at intervals of one second. If the speed of sound in air is $340 \, ms^{-1}$,the distance between the cliffs is .... $m$

$A$ tuning fork makes $256$ vibrations per second in air. When the velocity of sound is $330\, m/s$,the wavelength of the tone emitted is ... $m$.

The apparatus used to determine the velocity of sound in a gas is:

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