Is air a gas or liquid?

Answer 1

Air is a mixture of a number of gases, including nitrogen, oxygen, water vapor (a vaporized liquid is a gas), a little bit of carbon dioxide, argon, and trace amounts of other "noble" gases such as neon, krypton, etc. Thus, it's not completely correct to refer to air as "a" gas since, truly, it's a mixture of many. In thermodynamics, certain types of "heat engines" utilize air or other gases as the "working fluid." That's the material which the heat engine uses (or sometimes recirculates) while converting part of the input heat to mechanical work. One such engine is the "Otto cycle," an approximation of which is found under the hood of a gasoline-fueled automobile. Air flows in, heat is added (by combustion of gasoline with the air), and air flows out. Actually, the "air" which flows out -- the exhaust -- is no longer, strictly speaking, air. Most of the oxygen in the air has combined with the hydrocarbon fuel to produce carbon dioxide and water vapor. Thus, exhaust is essentially air, minus the oxygen, plus all the other gases that originally were there, plus additional carbon dioxide and water vapor. Oh, and plus some small amounts of other compounds, the "pollution."

Answer 2

Air is a liquid by far only hot air is a gas.

:D

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Answer 3

Air can be a gas or liquid if cooled enough.