Which observation most likely indicates that only one chemical change has taken place?1 The change cannot be reversed.2 The shapes changes 3states of matter 4changes a reaction occurs.

Answer 1

The observation that the change cannot be reversed most likely indicates that only one chemical change has taken place. This is because a chemical change involves the formation of new substances with different properties from the original substances, and this change cannot be undone. Changes in shape or state of matter can be physical changes that do not involve the formation of new substances, while a reaction occurring or changes in reaction conditions may involve multiple chemical changes.