Answer: solids.
Step-by-step explanation:
1) These are some values of the speed of sound in different media:
In air 343 m/s (approximate as it depends on the temperature and humidity)
In water 1,484 m/s
In iron 5,120 m/s
In diamond 12,000 m/s
2) Sound waves are disturbances (pulses) that propagates by the collision of particles in the media.
Since, the partilces in solids are closer than the particles in liquids, and these are closer than the particles in gases, the order of the propagation of the sound is:
Faster in solids than in liquids, faster in liquids than in gases.