Which type of wave moves particles of the medium parallel to the direction of wave propagation?

The type of wave that moves particles of the medium parallel to the direction of wave propagation is a longitudinal wave. In a longitudinal wave, compressions and rarefactions occur as the wave travels, causing particles to oscillate back and forth along the same direction as the energy of the wave. This motion can be observed in sound waves, where areas of high pressure (compressions) alternate with areas of low pressure (rarefactions) as the sound travels through a medium, such as air.

Transverse waves, on the other hand, involve particle motion that is perpendicular to the direction of wave propagation, such as in light waves or waves on a string. Surface waves include both longitudinal and transverse motion, typically seen in ocean waves. Standing waves, which are formed by the interference of two waves traveling in opposite directions, do not involve net transport of particles in the direction of the wave's motion, but rather create regions of high and low amplitude. Consequently, longitudinal waves are specifically characterized by the parallel motion of particles and the direction of energy transfer.