Question

why does sound travels faster in the solids,though, it has the highest density?

Answer 1

Sound travels faster in solid compare to liquid or gas:
Reason:
 Answer is very simple but first you need to know "How does sound travels ?".
Sound is  a wave (a wave is an oscillation accompanied by a transfer of energy that travels through a medium).
Sound moves only by passing  the energy to its neighbours molecules.this is known as the collision.
As we know that molecules in solids are more closer to each-other than a gas or liquid,because its Density is higher than gas or liquids. So more collisions occurs in less time.
Inshort:
Sound travels through a medium and solids provide a good medium.
Note:-
In space there is no medium so the astronauts can't talk by speak. 

Answer 2

Sound is a form of energy. Sound requires medium to travel, by transferring energy to neighbour particles in that medium in which the sound travels. Solids have particles tightly and closely packed. So when sound travels through solids, energy gets transferred fastly as compared to in liquids and gases. So, sound travels fastest in solids, than liquids and gases.
Speed of sound in solid (iron) = 5130 m/s.
Speed of sound on water ( at 20°C ) = 1480 m/s
Speed of sound in air = 330 m/s.