In the lung's alveoli, there are four gases mixed together: O2, carbon dioxide, nitrogen, and water vapor

At a normal barometric pressure of 760 mm Hg, alveolar O2 exerts a partial pressure of 100 mm Hg, CO2 40 mm Hg, and water vapor 47 mm Hg. What is the alveolar partial pressure of nitro-gen?
a. 187 mm Hg
b. 713 mm Hg
c. 660 mm Hg
d. 573 mm Hg

ANS: D
Dalton's law describes the relationship among the partial pressure and the total pressure in a gas mixture. According to this law, the total pressure of a mixture of gases must equal the sum of the partial pressures of all component gases. Moreover, the principle states that the partial pressure of a component gas must be proportional to its percentage in the mixture.