Which indicator most likely suggests that a chemical change is taking place?

The following are the indicators that there are chemical changes that took place:

Formation of a gas
* When gas bubbles are formed it is often a sign that a chemical reaction is taking place.

Formation of heat and light together
*When heat and light are given off together it is often a sign that a chemical reaction is taking place.

Formation of a precipitate
*A precipitate is a solid that appears after two liquids are mixed together.

Color change

Temperature change

From our previous experiment, we examined how many drops a penny can hold - and place drops of salt water on the penny after recording 5 trials each, take the average of each solution.