Which of the following is the best way to be certain that a chemical reaction has occurred?

• A. Detect the production of gas bubbles.
• B. Observe the formation of a new substance with different properties from the reactants.
• C. Notice a change in color of the solution.
• D. Measure a change in temperature of the mixture.

Answer: (B)

Verified step by step guidance

1. Understand that a chemical reaction involves the transformation of reactants into one or more new substances with different chemical properties.
2. Recognize that some signs like gas bubbles, color change, or temperature change can indicate a reaction but are not definitive proof on their own, as they might also result from physical changes.
3. Focus on the formation of a new substance with properties different from the original reactants, as this is the most reliable evidence of a chemical reaction.
4. Consider that detecting a new substance can involve observing precipitates, changes in odor, or other unique characteristics that were not present before.
5. Conclude that the best way to be certain a chemical reaction has occurred is to observe the formation of a new substance with different properties from the reactants.