A change of one substance to another, like burning or rusting?

• A. Conservation of mass
• B. Atom
• C. Chemical change
• D. Protons

Answer: (C)

A chemical change is when one substance becomes a different substance with new properties. In chemical changes, the atoms in the starting materials rearrange to form new compounds, so the substance you end up with has a different identity. Burning a fuel, for example, produces substances like carbon dioxide and water, not the original fuel, and rusting iron forms iron oxide with different characteristics. You can often notice clues such as a color change, a new odor, gas production, or a solid forming, all signaling that new substances have been created. The other ideas aren’t describing the transformation itself: conservation of mass is about mass staying the same during reactions, not what kind of change is happening; an atom is a basic particle involved in the process but doesn’t define the change; protons are subatomic components that don’t typically change in everyday chemical reactions.