At atmospheric pressure a balloon contains 2.00 l of nitrogen gas how would the volume change \

The complete question; At atmospheric pressure a balloon contains 2.00 l of nitrogen gas, how would the volume change if the kelvin temperature was only 75 % of its original value? 
 The change in volume would be;
original volume × percentage 
= 2 ×0.75 = 1.5 L
Thus the volume would change by 1.5 L

You know how the first one if filled up like the objects do the same but with the other categories

The answer is 323 g.