Final answer:
Among the options provided, the indication that a chemical reaction has occurred is the reaction with substance Y to form a gas or a white precipitate, which shows a chemical change has taken place due to the formation of a new substance.
Step-by-step explanation:
To provide a summary of the results for a chemical reaction and determine which of the following indicates a reaction has occurred, we can look for visual clues. Certain changes can confirm the occurrence of a chemical reaction. Among the options provided, reacted with substance Y to form a gas or white precipitate is an indication that a chemical reaction has occurred. This is because the production of a gas or a precipitate is a sign of a chemical change, which could indicate new substances being formed during the reaction process. Other signs of a chemical reaction, not necessarily mentioned in the options, include a change in color, the emission of light or flame, a noticeable temperature change, and a solid precipitate forming in the reaction.