Part of the answer you are looking for may be- Molecules overcome attractions easily and at high temperatures, move faster- (paraphrased from Google) Since the question asked was not provided with the statements as proposed in the original question, I cannot give you an exact answer. I did what i could do, hope this helps!
Multiply the volume by the density. 1 ml = 1 cm^3
1.11 g/cm^3 * 1 cm^3/mL * 386 mL = 428 g
All your units cancel out except for g which is what you would expect since you want units of mass.
Answer:
44.28 grams.
Explanation:
Let us write the balanced reaction:
As per balanced equation, six moles of fluorine gas will give four moles of PF₃.
The mass of PF₃ required = 120 g
The molar mass of PF₃ = 88g/mol
Moles of PF₃ required =
The moles of fluorine gas required = 
the mass of fluorine gas required = moles X molar mass = 0.91x38 = 34.58g
Now this much mass will be required if the reaction is of 100% yield
But as given that the yield of reaction is only 78.1%
The mass of fluorine required = 
Air is a mixture of gases (and some dust) because the gases (oxygen, nitrogen, carbon dioxide, etc.) do not combine chemically into other compounds. Just like a mixture of salt & pepper doesn't combine into some other thing.
The mixture is homogenous if it consists only of gases. If dust is mixed in the mixture is heterogeneous (dust is solid matter, gas is gas) A heterogenous mixture is one of different types of matter.
Separating one gas from the other is different for each gas and a complicated matter.
