A sound wave in air is (pick those answers that are appropriate) Bulk motion of the air at the speed of sound from its source to the detector or your ear. A propagating compression of the air followed by a \"rarefaction\" when the density drops, with the denser regions separated by a wavelength moving through the gas A disturbance that locally produces a change in pressure at the frequency of sound, but if you took a snapshot picture would show dense regions separated by a wavelength. A movement of molecules locally to reduce or increase the pressure, but no bulk motions of air. Solution There is no bulk motion of air, Sound propagates by compression and rarefaction of air locally with both separated by wavelength. Due to compression and rarefaction pressure changes and a pressure wave forms which moves in the direction of sound. So part 1 is false rest is true .