For Mass changes when a reactant or product is a gas, which option best supports this Unit 4.3 objective: Explain why the mass of a metal oxide may be greater than the mass of the metal when oxygen reacts with the metal?

The correct option is The total mass of reactants equals the total mass of products.

The correct option is The total mass of reactants equals the total mass of products. The total mass of reactants equals the total mass of products is correct because it directly supports the approved learning objective to explain why the mass of a metal oxide may be greater than the mass of the metal when oxygen reacts with the metal. The reasoning belongs to Mass changes when a reactant or product is a gas within Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations, so it should not be confused with nearby quantitative ideas such as mass, moles, concentration, yield, atom economy, or gas volume unless those are named in the objective. Use the focus term metal oxide to keep the answer aligned with AQA GCSE Chemistry 8462 Unit 4.3. The other options are weaker because they either use the wrong formula, the wrong unit, a vague relationship, or the wrong quantitative context.