Final answer:
Sound waves are an example of longitudinal waves, where particles move parallel to the wave's direction of travel. In contrast, electromagnetic waves like radio, light, and X-rays are transverse waves with perpendicular oscillations.
Step-by-step explanation:
An example of a longitudinal wave is c) Sound waves. Longitudinal waves are characterized by particle motion that is parallel to the direction of wave propagation.
In the case of sound waves, variations in pressure move through the medium (such as air or water) parallel to the direction the wave is traveling. In contrast, electromagnetic waves, such as radio waves, light waves, and X-rays, are all examples of transverse waves, where the oscillations are perpendicular to the direction of wave travel.