Which properties of a medium are responsible for propagation of wave through it ?

The property of a medium necessary for wave propagation is -

During propagation of sound wave through air medium

The sound wave propagates through

Two particles of a medium are vibrating due to a wave propagating through the medium. If the phase difference between these particles is (pi)/(3) and distance between the particles is 10 cm then calculate the wavelength of wave.

What should be the properties of the medium for producing sound waves ?

The medium for wave propagation should have the property of

Which type of waves do not require a material medium for propagation?