Which observation would indicate that a chemical reaction occurred?

• A. A color change is observed in the substance.
• B. The substance is crushed into smaller pieces.
• C. The temperature of the substance is lowered without any other change.
• D. The substance is dissolved in water.

Answer: (A)

Verified step by step guidance

1. Understand that a chemical reaction involves the formation of new substances with different properties from the original substances.
2. Recognize that physical changes, such as crushing a substance into smaller pieces or dissolving it in water, do not produce new substances; they only change the form or state.
3. Note that a temperature change alone, without other changes, can be physical and does not necessarily indicate a chemical reaction.
4. Identify that a color change often indicates a chemical reaction because it suggests that new substances with different properties have formed.
5. Conclude that among the given options, observing a color change is the best indicator that a chemical reaction has occurred.