Answer:
D.) the density changed
Step-by-step explanation:
This would be the answer because it is a specific amount of Nitrogen undergoing a physical change. Since the color and boiling point don't influence a change in volume, those are ruled out. Also, nitrogen's molecular mass never changes, so that would not make sense either. But if the density, which is mass/volume, has changed (more specifically decreases) then it means the volume has increased.
Hope this helps.