Final answer:
The fastest speed of sound is achieved in a medium with low density and high stiffness, making option B the correct answer. This is because low density means less mass to move and high stiffness indicates less compressibility.
Step-by-step explanation:
The speed of sound varies depending on the medium it travels through; specifically, it is influenced by the medium's rigidity (or stiffness) and density. A medium that is more rigid will allow sound to travel faster since the particles are less compressible and the sound energy can be transferred more efficiently. Conversely, the greater the density of the medium, the slower the speed of sound, because there is more mass that the sound waves have to move in transferring energy. Comparing the given options, low density, high stiffness will create the fastest speed of sound; therefore, the correct answer is option B. Sound travels faster in such a medium because the low density means there is less mass for the sound energy to move, and the high stiffness means the medium is less compressible, facilitating faster transmission of sound.