Sound waves travel at different speeds depending on the medium. In solids, sound waves travel the fastest because the molecules are tightly packed, allowing for efficient transmission of vibrations from one molecule to the next. This close proximity facilitates rapid propagation of sound waves. In liquids, the molecules are less densely packed than in solids, resulting in slower sound transmission. In gases, the molecules are spaced far apart, causing the slowest speed of sound as the vibrations take longer to travel from one molecule to another. In a vacuum, there are no molecules to transmit sound, so sound waves cannot travel at all.

For example, at room temperature, sound travels at about 343 meters per second in air (a gas), approximately 1,480 meters per second in water (a liquid), and around 5,960 meters per second in steel (a solid). Hence, the correct answer is; option [A] In solids.