Question

why in steel the speed of sound in highest

Answer 1

Particles that return to their resting position quickly are ready to move again more quickly, and thus they can vibrate at higher speeds. Therefore, sound can travel faster through mediums with higher elastic properties (like steel) than it can through solids like rubber, which have lower elastic properties.

Answer 2

Sound need a medium to travel and carried through particle.
More the particle,the more easy is travelling at faster is the speed and steel is solid and have no intermolecular spaces, so speed in steel is highest.