Final answer:
The balanced chemical equation among the provided choices is '2Na (s) + Cl₂ (g) → 2NaCl (s)', as it has an equal number of each type of atom on both sides and adheres to the law of conservation of mass.
Step-by-step explanation:
When looking at the provided equations, a balanced chemical equation has an equal number of each type of atom on both sides of the reaction. For instance, in the equation '2Na (s) + Cl₂ (g) → 2NaCl (s)', there are two sodium atoms on the reactants side and two sodium atoms on the products side; likewise, there is one diatomic chlorine molecule (which contains two chlorine atoms) on the reactants side and two chlorine atoms within the two NaCl units on the products side.
This understanding is based on the recognition that certain elements exist as diatomic molecules, specifically the seven essential diatomics: H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂. This equation is, therefore, properly balanced. Looking at the other examples provided, it is clear that a balanced chemical equation ensures the law of conservation of mass is upheld by having the same number of each atom on both sides of the equation.