Which of the following is not a common sign of a possible chemical reaction?

A. Dissolved precipitate

B. Formation of bubbles

C. Change in odor

D. Warming or cooling

The answer is C. Change in odor.

There are several signs of chemical reaction:

1. Dissolved precipitate.

2. Formation of gas (bubbles).

3. Change of color.

4. Change of temperature (warming or cooling).

5. Production of energy.

Among these signs, there is no change in odor, which is, thus, the right choice.