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?

  Options: 
 A. photographs of reactants and products
 B. listing of masses of reactants and products
 C. listing of time from start to finish of reaction
 D. photograph of a flame produced when the chemicals reacted 
Answer: D