Figure 2 shows how the temperature of the water varied with time.

What is the name of the process that is taking place between points A and B?
Give a reason for your answer.

The graph shows that as time increases, the temperature initially rises. This is the water heating up. Between points A and B, time continues to pass (meaning energy is still being supplied), but the temperature remains constant. This flat section on a heating curve indicates a change of state. Since the water was being heated, this change of state is from liquid to gas, which is called boiling or vaporisation. The energy being supplied is used to break the bonds between water molecules (latent heat of vaporisation) rather than increasing their kinetic energy (temperature).