Sound in air propagates in form of:
(a) Longitudinal wave
(b) Transverse wave
(c) Both longitudinal and transverse wave
(d) Neither longitudinal nor transverse wave

(a) Longitudinal wave

Reason — The two kinds of waves in form of which sound travels in a medium are:

1. Transverse waves — The wave in which the particles of medium vibrate about their mean positions, in a direction perpendicular to the direction of propagation of the wave.
   Transverse waves can only be produced in solids and on the surface of liquids. They cannot be produced inside liquids and inside gases.
2. Longitudinal waves — The wave in which the particles of medium vibrate about their mean positions, in the direction of propagation of sound.
   Longitudinal waves can be produced in solids, liquids as well as gases.

Hence, sound in air propagates in form of longitudinal wave.