Answer:
3; balanced; the same number of; The Law of Conservation of Mass
Explanation:
In a physical model that shows the reaction of zinc metal and hydrochloric acid (hydrogen chloride), 3 different colors are needed to represent the different types of atoms. This represents a balanced equation because there are the same number of atoms of each element on the reactants and products side of the equation. The scientific principle represented here is The Law of Conservation of Mass .