Which is the most important question for deciding if a chemical reaction has occurred?
was there a change in the size?
was any heat energy given off?
what is the density of the substance?
what is the texture of the substance?

Was any heat energy given off?

Explanation:

A chemical reaction may exothermic (heat is given off) or endothermic (heat is absorbed). Size, density or texture of the substance are strictly physical properties which cannot confirm that a chemical reaction has transpired in the sample. The evolution of heat ultimately confirms that a chemical process has taken place.

i think the answer is terrae but not 100 percent sure. ▓▬▬ §