Question

What is a longitudinal wave? In which medium: solid,liquid or gas, can it be produced?

ICSE Class 9 Physics Chapter Propagation of Sound

Answer 1

wave in which particles of a medium vibrate about their mean positions, in the direction of propagation of sound is called longitudinal waves...
it can be produced in all-solid liquid gases

Answer 2

A type of wave motion in which the particles displacement of wave is parallel to the direction of wave propagation is called a longitudinal wave. It can be produced in solid, liquid as well as gases.