Marcia is given an incomplete chemical equation that includes the number of nitrogen atoms present in the products of the reaction. how can she conclude that the reaction started with three nitrogen atoms?

If the products contain 3 nitrogen atoms, then so did the reactants since overall mass is conserved in a chemical reaction.

Explanation:

an ion is a charged atom or molecule. it is charged because the number of electrons do not equal the number of protons in the atom or molecule. an atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom.