In which medium does sound travel fastest.And why?

Dear Student,
Speed of sound depends on the density of the medium. Higher the density of the medium, faster is the sound. Thus, speed of sound is minimum in air and maximum in solids, particularly, metals. Among metals, Osmium is the metal having highest density. However, Osmium is only available in traces. Among the widely used metals, speed of sound is highest in steel.

Regards