Which of the following changes does NOT describe a physical change?

The burning of wood to ash is a chemical change because it involves a reaction that alters the molecular structure of the wood. When wood burns, it reacts with oxygen in the air, producing new substances such as carbon dioxide, water vapor, and ash, which have different properties from the original wood. This change is irreversible under normal conditions, meaning that you cannot simply reverse the process to get back the original wood.

In contrast, the other options pertain to physical changes, which are characterized by changes in physical properties without altering the chemical composition of the substance. For example, changing shape, melting ice to water, or transforming from a liquid to a solid are all physical changes where the substance retains its chemical identity throughout the process.