What is the density of a medium?

the measure of how fast a sound wave can travel through the medium
the amount of mass in a given amount of space, or volume
the ability of the medium to bounce back after being disturbed
the amount of heat energy that can be absorbed by the medium

The correct answer is: the amount of mass in a given amount of space, or volume. Density is defined as mass per unit of volume, expressed in kilograms per cubic meter (kg/m3) in the SI system. It is a physical property of matter that helps to describe how tightly packed the particles are within a substance. The denser a medium is, the slower sound waves can travel through it.