Question

in a longitudinal wave, how do particles move? *
up and down (perpendicular with the direction of the wave)
back and forth (parallel to the direction of the wave)
in a circle

Explanation:

In a longitudinal wave, particles move parallel to the direction of the wave propagation. This is in contrast to transverse waves where particles move perpendicular to the wave direction.

Answer:

Back and forth (parallel to the direction of the wave)