Final answer:
Both B. H₂ + O₂ → H₂O and C. Mg + Cl₂ → MgCl₂ correctly demonstrate the conservation of mass in a chemical reaction because they are balanced, showing equal numbers of each type of atom on both sides of the equation.
Step-by-step explanation:
The question you've asked is about the conservation of mass in chemical reactions, specifically which of the provided equations demonstrates that the total mass during a chemical reaction stays the same. By the Law of Conservation of Mass, the mass of the reactants must equal the mass of the products in a chemical reaction.
Looking at the given equations:
2Na + 2H₂O → NAOH + H₂ is not correct; it is a typo and not a balanced reaction.
H₂ + O₂ → H₂O is balanced and shows the conservation of mass.
Mg + Cl₂ → MgCl₂ is balanced and conserves mass.
NaOH + MgCl2 → NaCl + M9OH has a typo and 'M9OH' should be 'Mg(OH)₂'; also, the equation is not balanced.
Correct Answer: B. H₂ + O₂ → H₂O and C. Mg + Cl₂ → MgCl₂ both demonstrate that the total mass during a chemical reaction stays the same as they are balanced chemical equations.