Question 2
In activity 3.1.10 an unopened soda bottle cannot be squeezed while an identical bottle of water can. Why?
The right answer is the one marked above.
Carbon dioxide is held above the liquid under high pressure. That pressurised gas is what makes the bottle hard, and it escapes the moment the cap is opened.
The bottles are deliberately the same kind and hold the same volume of liquid, so thickness and density are ruled out by the design of the activity.