The composition of moist air is given on a molar basis as 78 percent N2, 20 percent O2, and 2 percent water vapour. Thus, when determining the mass fractions of air components, we can say that: (a) The molar mass of the mixture is 15.0 kg/kmol.
(b) The molar mass of the mixture is 7.2 g/mol.
(c) The molar mass of the mixture is 15.0 kg/kmol only for a temperature of 273.15K and a pressure of 1 atm.
(d) None of the above.

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