* Size of molecules (1): The size of molecules doesn't change during a phase transition. Water molecules are the same size whether they are in liquid or gaseous form.

* Kinetic energy of molecules (3): While kinetic energy plays a role in boiling, it doesn't fundamentally *change* during the phase transition at a constant temperature. The average kinetic energy of molecules in the liquid state at the boiling point is roughly the same as the average kinetic energy of molecules in the gas state at the same temperature.

* Distance between molecules (2): This is the key difference. In a liquid, molecules are closely packed and interact strongly. When a liquid boils, the molecules gain enough energy to overcome these attractions and break free from the liquid state. In the gas phase, the molecules are much further apart, with far weaker interactions.

In summary: Boiling is about the molecules gaining enough energy to overcome the attractive forces holding them together in the liquid state, increasing the distance between them and creating a gas.