Which observation most likely indicates that only a chemical change has taken place? (1 point)
O States of matter changes
O A reaction occurs.
O The change cannot be reversed.
O The shape changes.
The correct answer is: A reaction occurs.
The observation that most likely indicates that only a chemical change has taken place is when a reaction occurs.
To determine if a chemical change has occurred, we need to look for evidence of a chemical reaction. Here's how you can identify a chemical reaction:
1. Look for the occurrence of a reaction: If a reaction has taken place, it means that there has been a chemical change. This could be indicated by the appearance of bubbles, a color change, or the formation of a precipitate.
2. Check if the change can be reversed: Physical changes, such as changes in states of matter or changes in shape, can usually be reversed. However, chemical changes cannot easily be reversed. So, if the change cannot be reversed, it is more likely that a chemical change has occurred.
3. Consider if the change involves the breaking or forming of bonds: Chemical reactions involve the breaking and forming of chemical bonds between atoms. If you observe changes in the composition and structure of molecules, it is a strong indication of a chemical change.
In the given options, the observation "A reaction occurs" is the most direct evidence of a chemical change. This indicates that there has been a chemical reaction, involving the breaking and forming of bonds between atoms or molecules.