Which of the following is an example of physical change?

A physical change is defined as a process where the substance's chemical composition remains unchanged, even if its state or appearance alters. When water changes into steam through boiling, it undergoes a phase transition from liquid to gas. The molecules remain H2O throughout this process, making it a reversible physical change without any new substance being formed. In contrast, the formation of milk from curd involves fermentation, which alters chemical properties permanently. Similarly, browning of an apple is a chemical reaction (oxidation), and digestion involves breaking down complex molecules into simpler ones chemically. Therefore, changing water into steam is the only example where no new chemical substance is produced.