The student hypothesized that adding lemon juice to an apple would create a chemical change, as the citric acid in lemon would dissolve the apple. In an experiment, one apple was left untreated while lemon juice was added to another. After 5 minutes, the untreated apple had a brown spot from oxidation, representing a physical change, while the lemon-treated apple looked clean, indicating a chemical change as the lemon and apple substances combined. The conclusion was that both a chemical and physical change occurred.