The options are missing in the question, so I am going to answer it in a general way.
There are several indicators of chemical reactions. They are:
Gas Bubbles Appear
Formation of a Precipitate
Color Change
Temperature Change
Production of Light
Volume Change
Change in Smell or Taste
Depending of what kind of reaction is occurring which indicator appear. For example in combustion reactions the temperature increase because they are highly exothermic; and in electrolysis of water, bubbles of molecular oxygen and molecular hydrogen are generated.
Flammability the others don't have to do with the chemical composition of an object. (density and color have to do with the physical properties of a substance.)'