An example of a longitudinal wave is?

A longitudinal wave is characterized by the motion of particles in the medium being parallel to the direction of the wave's propagation. In this type of wave, compressions and rarefactions occur as energy moves through the medium.

Sound waves are a perfect example of longitudinal waves. When a sound wave travels through the air, the air particles vibrate back and forth along the same direction that the sound wave is moving. This results in areas where particles are closer together (compressions) and areas where they are spread apart (rarefactions).

In contrast, light waves and radio waves are types of electromagnetic waves, which do not require a medium to travel through and involve electric and magnetic fields oscillating perpendicular to the direction of wave travel. Water waves involve a combination of longitudinal and transverse motions, as the surface moves in circular paths. Thus, sound waves are clearly the correct choice as they exemplify the fundamental properties of longitudinal waves.