You know that Density = Mass/Volume, right? In symbols,
D = m/V.
If mass (m) is constant, let’s replace m with the symbol k to represent a constant. Then,
D = k/V or D ∝ 1/V
Density and Volume are inversely proportional. When one goes up, the other goes down and vice versa.
Mass is an extrinsic property because it depends on how much of the material you have. The more material you have, the greater its mass will be.