Answer:-
Medium in which the sound waves are travelling.
Explanation:-
To understand this first we need to know that there are 2 types of waves; Mechanical waves and Electromagnetic waves.
Sound waves are mechanical waves meaning they need a medium to propagate. So this clarifies that they will obviously depend on the properties of the medium.
As far as the topic of speed is concerned;
sound travels fastest in solids than through liquids and gases because the molecules of a solid are closer together and, therefore, can transmit the vibrations (energy) faster.
Link:-
https://youtu.be/yF4cvbAYjwI
Hope it helps, feel free to clarify any confusion/confusions.
