What determines whether a physical change occurs in a substance?

A physical change occurs when there is a modification in the physical properties of a substance, without altering its chemical composition. This includes changes in size, shape, state of matter (such as melting, freezing, or evaporating), and other observable characteristics. While the chemical composition remains constant, changes can be seen in how the substance looks or behaves under physical conditions.

Physical appearance alterations inherently differentiate a physical change from a chemical change, ensuring a clear distinction between the two types of changes. For instance, when ice melts into water, the substance remains H2O, but its form and appearance have changed from a solid to a liquid.

The other options involve potential factors that can affect how a substance behaves but do not fundamentally define physical change. For example, environmental conditions and temperature can influence a substance's state or appearance but do not inherently cause a physical change themselves. Similarly, a change in chemical composition indicates a chemical change rather than a physical one. Therefore, the alteration of physical appearance is the key determining factor for identifying physical changes.