The equation will balance because the number of hydrogen atoms and atoms is in the reactants and in the products in this case is 2.
Reaction balancing is a method used in several areas of Chemistry to determine the amount of matter of each of the substances participating in the reaction, as well as to establish the existing proportions between the components.
So, since you must have the same amount of sodium and chlorine on each side of the reaction, then you have multiplay the NaCl for 2.
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