Answer:
She can conclude that the reaction started with three nitrogen atoms because she can be based in the law of conservation of matter which states that the amount of matter in a system is conserved: there were three atoms of nitrogen in the reactants and they produced three atoms of nitrogen.
Explanation:
In science, a law is a general statement that explains a large number of observations. One law that provides the foundation for understanding in chemistry is the law of conservation of matter: it states that in any given system that is closed to the transfer of matter (in and out), the amount of matter in the system stays constant, or in other words, the amount of matter in a system is conserved.
So, in this case, for Marcia to conclude that the reaction started with three nitrogen atoms, she can be based in the law of conservation of matter, and because the matter of that system is conserved, there were three atoms of nitrogen in the reactants and they produced three atoms of nitrogen.
