A researcher is measuring changes in the density of the upper atmosphere over time. Which units should be used for the density measurements?

lbm/ft³ or psi/ft

Explanation:

The description in the question shows the density to measured is that of gases (upper atmosphere). The density of a gas can be described as the mass of the gas divided by the volume of the gas at a certain temperature and pressure. It's unit can be represented as lbm/ft³ or psi/ft.

NOTE:

"lbm" means "lean body mass" which is a unit for mass or weight and can be described as the pound mass

"psi" means "pound per square inch"; is also a unit for mass or weight

each chemical family is represented as a group or column on the periodic table. based on chemical properties, there are 6 types of chemical families. group 1 represents alkali metals, group 2 represents alkaline earth metals, groups 3 to 12 represent transition metals, groups 13 to 16 represent non-metals and other metals, group 17 represents halogens and group 18 represents noble gases.