The change from a to b is a physical change. When ice melts, it changes from a solid to a liquid. This is a change in the state of matter, but the chemical composition of the water does not change.

The change from b to c is a chemical change. When water boils, the water molecules break down into hydrogen and oxygen gas. This is a change in the chemical composition of the water.

Here are some more details about the two types of changes:

* Physical changes:

* Do not change the chemical composition of a substance

* Can be reversed

* Examples include melting, freezing, boiling, and condensing

* Chemical changes:

* Change the chemical composition of a substance

* Cannot be reversed

* Examples include burning, rusting, and rotting