7. the speed of a sound wave depends mostly on

option C: the medium through which the wave travels.

Justification:

1) The sound is a wave.

2) The speed of the sound depends on the medium through which it travels.

3) The sound travels the slowest in gases and the fastes in solids. The speed of sound in liquids is faster than in gases and slower than in solids.

4) 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

Those data of the speed of sound in different media show that the speed of sound waves depends mostly on the medium through which the wave travels.