Final answer:
Mixtures are physical blends of two or more substances that retain their own identity and properties. Polyesters are an example of mixtures that undergo a chemical reaction and harden when mixed.
Step-by-step explanation:
Mixtures are physical blends of two or more substances that retain their own identity and properties. Unlike compounds, mixtures can be easily separated back into their original components. One example is polyesters, which are a type of mixture that undergoes a chemical reaction when mixed and hardens.