Air is about 78% nitrogen gas (N2) by mass. The molar mass of nitrogen gas is 28.0 g/mol. A 100.0-g sample of air contains how many moles of nitrogen?

2.8

3.6

28

78

We can easily use the given values in the problem statement as follows:

Mass of nitrogen = 100 (.78) = 78 grams

Moles of nitrogen = 78 g (1 mol / 28 g) = 2.7857 mol

Therefore, the correct answer from the choices listed above is the first option. Have a nice day.