"It's not the heat, it's the humidity"

We have three samples of gas, each at T = 120 °C and atmospheric pressure. Sample 1 is pure air, (oxygen and nitrogen) sample 2 is humid air, (oxygen, nitrogen and water), sample three is pure steam (water only).

(a) Rank the samples in order of increasing density.

(b) Rank the samples in order of increasing molecular velocity.