Final answer:
The strongest indicators of a chemical reaction are a change in color, formation of bubbles, and changes in temperature. These signal that a chemical reaction has taken place, with the formation of new substances with distinct properties from the reactants.
Step-by-step explanation:
When performing a chemical experiment, there are various observations that can indicate that a chemical reaction has occurred. The strongest indicators include: a change in color, the formation of bubbles indicating gas production, changes in temperature, and the formation of a precipitate. Specifically, if compound Q and Dark produce compound Santi with a different color from the reactants, it is a strong sign of a chemical change. Similarly, if bubbles appear, suggesting gas formation, especially when the reaction mixture is not boiling, this indicates a chemical reaction. Changes in temperature, whether increase or decrease, are also a sign of an energy transfer due to a chemical reaction.
If no change is observed, then it is likely that no chemical reaction has taken place, at least not one that can be detected through simple visual cues. Therefore, for Jack's experiment, the presence of a color change, formation of bubbles, or a temperature change would each be strong evidence that a chemical reaction between compounds Q and Dark to form Santi has occurred.