The graph shows the displacement of a medium when a longitudinal wave travels through the medium from left to right. Positive displacements correspond to motion to the right. Which point corresponds to the centre of the compression?

The graph shows the variation with the time of the displacement of a particle in a medium when a wave of intensity I travel through the medium. The Intensity of the wave is halved. Which graph now represents the variation of displacement with time? (The scale on all graphs is the same.)

Travelling waves of wavelength $32 \mathrm{cm}$ are created in a closed-open pipe $\mathrm{X}$ of length $40 \mathrm{cm}$ and an open-open pipe $\mathrm{Y}$ of length $50 \mathrm{cm}$. In which pipe or pipes will a standing wave be formed?