Question 2
In activity 15.2, once the balloon is connected to arm X and the knot undone, the water level in arm Y rises above the level in arm X. What does this tell us?
The right answer is the one marked above.
The compressed air in the balloon is at a higher pressure than the atmosphere. The pressure at the water surface in X therefore rises and pushes that level down.
If the two pressures were equal, the levels in both arms would stay equal — which was the situation before the balloon was connected.