Final answer:
The statement 'B- A new substance forms' exclusively describes a chemical change because it alters the composition of the original substance, unlike physical changes that do not change the chemical identity.
Step-by-step explanation:
The statement that describes all chemical changes but not physical changes is 'B- A new substance forms'. During chemical changes, the composition of the substance changes, creating a new substance with different chemical properties. Examples are the burning of gasoline, which turns into carbon dioxide and water, and the souring of milk, which involves the production of various new substances due to chemical reactions.
Other options like bubbles being produced or a color change can happen in both chemical and physical changes, hence they are not exclusive to chemical changes.
Phase changes, like water boiling into steam, are physical because they only involve changes in the state of matter without altering the chemical identity of the substance. Similarly, changes in color can also occur in physical changes when mixing substances that retain their original properties, like mixing different colored beads.