The speed at which a wave travels through a medium is determined by:

The speed at which a wave travels through a medium is fundamentally influenced by the characteristics of that medium, specifically its stiffness and density. Stiffness refers to the ability of the medium to resist deformation when a force is applied - a stiffer medium allows sound waves to travel faster because the particles are tightly packed and can transmit energy more efficiently. Density, on the other hand, relates to the mass of the medium; a heavier medium typically slows down the propagation of sound waves.

When both stiffness and density are combined, they directly determine the wave speed as described by the formula for the speed of sound, which is proportional to the square root of the stiffness divided by the density. This fundamental relationship explains why this answer is the most accurate in the context of wave propagation within different media.

Other factors such as frequency of the sound source and distance from the sound source do not directly impact the speed of sound in a medium; instead, frequency affects the wavelength and pitch of the sound while distance can affect intensity but not speed. Resistance and impedance play a role in how waves propagate in terms of energy loss and reflection, but they do not dictate the speed at which the sound wave travels through a medium. Thus, the correct understanding of the relationship between medium