Answer the following question given this paragraph: 

As you know, density is defined as the mass per unit volume of a substance. Since gases all occupy the same volume on a per mole basis, the density of a particular gas is dependent on its molar mass. A gas with a small molar mass will have a lower density than a gas with a large molar mass. Gas densities are typically reported in g/L. Gas density can be calculated from molar mass and molar volume.


Q: What is defined as the mass per unit volume of a substance?

 Choices:

- weight

- diameter

- height

- density

A:
density
