How would you find out the volume 8kg of nitrogen gas would be?
Can I ask what is your situation that makes you ask this question? Because I find it hard to understand how anyone is required to answer questions like this who hasn't the resources, e.g. a textbook, to attempt an answer.
It is pretty elementary and easy, and usually we require students here to show what they have tried.
You're asked for answers on something not done in class and that your textbook doesn't cover?
You will need a new textbook because this one will not take you far.
Maybe you are supposed to find out using google.
Anyway the shotest easist thing I found was here http://answers.yahoo.com/question/index?qid=20120226213423AAcKYhO
But just remember that there are a number of physical magnitudes and constants that it is just useful to remember. I do not practice what I preach enough, but one thing I most remember is the volume of a mole of gas at standard temperature and pressure.
In your book there is hopefully a section on 'Avogadro's hypothesis' 'molar volume' and the 'Gay-Lussac law of volumes'.