Answer:
Gas
Step-by-step explanation:
Mechanical waves- travel faster in solids & slowest in gases
Electromagnetic waves- travel fastest in empty space and slowest in solids.
Because they are so close, than can collide very quickly, i.e. it takes less time for a molecule of the solid to 'bump' into its neighborough. Solids are packed together tighter than liquids and gases, hence sound travels fastest in solids. The distances in liquids are shorter than in gases, but longer than in solids.