Final answer:
Psia stands for pounds per square inch absolute, which is a unit of pressure that includes atmospheric pressure in addition to the internal pressure of a system. The correct answer is option c:Pascals per square inch absolute.
Step-by-step explanation:
In the context of a rigid tank containing air at a pressure of 90 psia, the acronym psia stands for pounds per square inch absolute. This is a unit of pressure that takes into account the atmospheric pressure in addition to the pressure exerted by the air in the tank. The gauge pressure (Pg) would not include atmospheric pressure and is the pressure reading you would see on a gauge that measures the difference between the internal pressure and the atmospheric pressure.
However, the absolute pressure (Pabs) takes into account the atmospheric pressure (Patm) as well. Using Pascal's principle, the total, or absolute, pressure is calculated by Pabs = Pg + Patm, where Patm is approximately 14.7 psi at sea level. So when a pressure gauge shows any psi reading, the absolute pressure is the gauge reading plus the atmospheric pressure. For example, a tire gauge reading of 34 psi would actually reflect an absolute pressure of 48.7 psi when you add the atmospheric pressure.