A balloon filled with helium has a volume of 3.0 L when the temperature is 273 K and a pressure of 1 atm. When the temperature is raised to 546 K, the balloon’s new volume is 6.0 L and the pressure remains at 1 atm. Some students try to explain what has happened inside the balloon.

Student A: The volume of the gas has increased because the molecules of helium have gotten bigger.

Student B: No, the molecules are still the same size and the number of collisions are the same. They just have more space between them.

Student C: The size of the molecules of helium does not change but the molecules will be moving faster and hitting the walls harder causing the balloon to expand.

With which of the three students do you agree? Justify your reasoning.
You may agree with more than one student.