Ben and Jerry added small pieces of magnesium to hydrochloride acid. They noticed that bubbles formed, the test tube got hot, and the the magnesium disappeared. What is a sign that a chemical reaction has taken place in this experiment

The number of medals awarded to the track team during the season.

Your question is not clear but if you can explain yourself i would be glad to .  just trying to : ))

Ibelieve it is b. proton.hope my answer has you : )

In reversible reaction chemistry equilibrium is attained when the forward and reverse reactions are taking place at the same rate, thus, the concentrations of reactants and products remain the same. a reversible reaction is a chemical reaction where the reactants form products that, in turn, react together to give the reactants back. in irreversible reactions on the other hand, the reactants react to form the products, which cannot revert back into reactants.