Sound wave is travelling along positive x-direction. Displacement (y) of particles from their mean positions at position x-is shown in figure. Choose the correct alternative (s)

Velocity of particle is given by ${\mathrm{v}}_{\mathrm{p}}=-\mathrm{v}\left(\frac{\mathrm{dy}}{\mathrm{dx}}\right)$
Here, v is wave speed and dy/dx the slope.
At point E slope is positive, therefore, v_p will be along negative x-direction. 

Similarly, slope at D is zero. so the particle located at D has zero velocity.

Therefore, Excess pressure $\mathrm{dP}=-\mathrm{B}\cdot \frac{\mathrm{dy}}{\mathrm{dx}}$
At C slope is negative. Therefore, dP is positive i.e. particles located near C are under compression. 

At point D, slope is zero i.e., dP = 0