help with general chemistry?

Question

I'm trying to figure out some questions to study for a test .. can anyone help me out? ....Here they are :
1.) When do gases behave like real gases and when do they not?
2.) Why can we assume that the molecules of a gas occupy no volume and that there are no attractions or repulsions between molecules?
3.) The quantity of oxygen gas in a 34.0L balloon is increased from 2.7 grams to 5.3 grams at constant pressure. What is the new volume of the balloon?

Answer 1

1. Ideal conditions are high temperature and low pressure.
2. We normally handle gases well above their boiling point.
3. (5.3/2.7) x 34