Explain why changes of state are physical changes

A change in state (solid to liquid, or liquid to gas, or solid to gas, etc.) is a physical change because the chemical composition of the material does not change. It is still the same substance chemically. For example, ice and water and steam all have the same chemical formula: H2O.

Physical changes are those that have a change in "characteristics" therefore state change is when the state (solid, liquid, gas) are changed. 

In your answer you can put because state change is when the substance changes to a solid, liquid, or gas. 

sorry if its confusing... however chemical changes are when there is a rection between two interactions of substances and there is gas formed, along with heat, and is difficult to reverse. 

Answer(b)