The main difference between a radio wave and a sound wave is their different

Direction of oscillations

Explanation:

- Radio waves are part of the electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic field. Electromagnetic waves are transverse, which means that the oscillation (of the fields) occurs in a direction perpendicular to the direction of propagation of the wave.

Electromagnetic waves are also the only type of waves that can travel through a vacuum, since they do not need a medium to propagate.

- Sound waves are mechanical waves, which consists of periodic disturbances of a medium. Sound waves are longitudinal, which means that the direction of their oscillation occurs parallel to the direction of propagation of the wave, creating alternating regions of higher density (compressions) and lower density (rarefactions) of particles.

Mechanical waves, unlike electromagnetic waves, always need a medium to propagate.