The speed of sound in a medium is determined by

The speed of sound in a medium is given by the formula $v = \sqrt{\dfrac{E}{\rho}}$, where $E$ is the modulus of elasticity of the medium and $\rho$ is its density.

The modulus of elasticity $E$ represents the elastic property of the medium, which determines how quickly the particles return to their original position after being displaced.

The density $\rho$ represents the inertia property of the medium, which determines the resistance of the particles to acceleration.

Therefore, the speed of sound in a medium depends on both its elastic property and its inertia property.