Dry air (0% humidity) is approximately 78% n2, 21% o2, and 1% ar by moles. calculate the molar mass and density of dry air at stp. assume ideal behavior and use two significant figures in your answers.

For the first question, we calculate as follows with the basis of 100 mol dry air:

78 * 28 + 21*32 + 1*39.9 / 100
 
molar mass of air =28.959=28.96
 
For the second question, we calculate as follows:
 
Vapor density = molecular weight/2=14.48
Relative density= vapor density * density of hydrogen(0.089). = 1.29

The correct name for n3-ion should be azide.

And a) oxygen i believe