(N/A) The curve representing density or pressure variations with respect to distance for a sound wave is shown in the provided image.
$1$. Compression: These are the regions of high pressure and high density,represented by the crests of the wave.
$2$. Rarefaction: These are the regions of low pressure and low density,represented by the troughs of the wave.
$3$. Wavelength: It is defined as the distance between two consecutive compressions or two consecutive rarefactions.
$4$. Time-period: It is defined as the time taken by the wave to travel the distance between any two consecutive compressions or rarefactions from a fixed point.