The diagram above illustrates trapped air in a syringe placed in water that is gradually heated. It is observed that the piston rises as the temperature of the water rises. Which of the following statements explains this observation?

A. frequency of collision of trapped air molecules with walls of the syringe is more
B. molecules of trapped air expand more
C. speed of the trapped air molecules decreases
D. number of molecules of trapped air increases

Correct Answer: Option B

B. molecules of trapped air expand more