which observation most likely indicates that only a chemical change has taken place?

Question

1. a reaction occurs
2. the shape changes
3. states of matter changes
4. the change cannot be reversed

Answer 1

The observation that most likely indicates that only a chemical change has taken place is:

1. a reaction occurs

Chemical changes usually involve a reaction where substances are transformed into different substances, resulting in changes to their chemical properties. The other options (shape changes, state changes, and irreversibility) can occur in both physical and chemical changes, making them less definitive indicators of a chemical change.