The freezing of water is called a physical change because it involves a change in the state of matter without altering the chemical composition of the substance. When water freezes, it transitions from a liquid state to a solid state, forming ice. Throughout this process, the molecular structure of H2O remains unchanged; only the arrangement of the molecules is affected.
In a physical change, the substance retains its original properties even after the change occurs. For instance, ice can easily be melted back into liquid water, demonstrating that no new substance has been formed. This is different from a chemical change, where the original substance would transform into a new substance with different properties.
Overall, the freezing of water is a clear example of a physical change as it maintains the same chemical identity while varying its physical state.