Well I forgot to mention the percentage amounts to take into consideration. In this case we know there is more oxygen, which is 32.00 g/mol, and nitrogen molar mass plus oxygen molar mass is obviously greater.

It doesn't actually matter what percentage it is. As soon as you know air is a mixture of oxygen (M

_{r}=32) and other gases with M

_{r}s less than 32 then the density of air must be lower than that for oxygen. It wouldn't matter if air was 99.99% O

_{2} or 0.01% O

_{2} the density of air would still be lower. Obviously gases like Ar and CO

_{2} raise the density but that is negligible compared to N

_{2}.

We aren't adding 1 L, we're assuming densities at STP, which is 22.44 L. So the volume is 22.41, not 1.

That was just an example.

And a perfectly legitimate example. The question told you that 1 mole of gas occupies x litres, when you are working with density it doesn't matter how much gas you have the density will be the same, you could have assumed there to be 100 billion litres of gas or 0.00001 moles of gas it won't make a difference.

Yeah sorry for the mistake, I just get a little imaginative sometimes

I know it was just an example when you said 1 L, just trying to make you angry

LOL