The air in the troposphere is a(n)

element
compound
mixture

The answer is mixture. A mixture is a substance that is composed of a combination of different elements that are not chemically combined (and can be physically separated). The troposphere is the lowest layer of the earth’s atmosphere and where the weather condition occurs. This means the air is mixed with water vapor (that form clouds) and other impurities such as dust and aerosols.

aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.