Final answer:
The browning of an apple when exposed to air is a chemical change because new substances are formed during the enzymatic browning process, indicating a chemical reaction.
Step-by-step explanation:
When you cut an apple into slices and leave them in the open air, and they turn brown, it is an example of a chemical change. This browning process is called enzymatic browning and occurs because the apple's cells are damaged when sliced, exposing enzymes to oxygen in the air, which causes the apple to oxidize. This process changes the chemical composition of the apple, creating new substances, as indicated by the color change. Therefore, it is not merely a change in appearance; it is a transformation at the molecular level, making the browning of the apple a chemical reaction.