Which statement correctly describes the alveolar gas equation?

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The key idea is that PAO2 (alveolar oxygen tension) depends on the amount of oxygen a person is breathing and on how CO2 is produced and removed, with adjustments for humidity and the respiratory quotient. The alveolar gas equation expresses this by using the inspired oxygen fraction (FiO2) and the pressure available to oxygen after removing water vapor, which is driven by barometric pressure (Pb) minus the water vapor pressure (PH2O), and then subtracting a CO2 term scaled by the respiratory quotient (R). In practical form, PAO2 ≈ FiO2 × (Pb − PH2O) − PaCO2 / R. This shows why the statement that includes FiO2, Pb, PH2O, PaCO2, and R is correct: all these factors shape the alveolar oxygen tension. The other statements miss essential components: PAO2 is not independent of FiO2, CO2 alone does not determine PAO2, and barometric pressure is a relevant part of the calculation.