Certify Teacher Practice Test

The correct answer highlights that moldy bread undergoes a chemical change because new substances are formed through the biological processes of the mold. When bread becomes moldy, the mold spores develop and metabolize the bread, leading to the creation of byproducts that are fundamentally different from the original ingredients of the bread. This transformation not only alters the bread in terms of its appearance and smell but also in its chemical composition, as the organic matter in the bread breaks down and new chemical compounds emerge due to the actions of the mold.

Physical changes typically involve alterations in form or appearance without changing the substance's chemical nature, such as cutting or tearing. In this case, while you can see the visible mold, the original substance (bread) cannot be fully restored to its original state because the chemical nature has been altered. The answer emphasizes the irreversible nature of the changes that occur, solidifying why it is classified as a chemical change rather than a physical one.