Recall that density represents the amount of mass per unit of volume. And when it comes to our density formula, its density equals mass over volume. Now gases are much less dense than solids and liquids. So when it comes to their density, we're going to say their density is in grams per liter.
M here is still mass of the gas in grams. And then here volume V will be in liters. So again, when it comes to density, it's massvolume and gas is being much less dense. Don't use grams per milliliter or grams per centimeter, but instead use grams per liter.