photographs of reactants and products listing of masses of reactants and products listing of time from start to finish of reaction photograph of a flame produced when the chemicals reacted
I gave my students this multiple choice question: A student concludes that a chemical reaction performed in a classroom investigation was exothermic. To communicate the validity of this conclusion, which would make the best visual evidence in a presentation?

Only one answer is correct among these 4 choices:
- photographs of reactants and products
- listing of masses of reactants and products
- listing of time from start to finish of reaction
- photograph of a flame produced when the chemicals reacted

Could you tell me which one is correct?

photograph of a flame produced when the chemicals reacted