Final answer:
In the reaction 2 Mg + O₂ → 2 MgO, there are two magnesium atoms and two oxygen atoms in both the reactants and products, hence observing the law of conservation of mass.
Step-by-step explanation:
The chemical reaction 2 Mg + O₂ → 2 MgO shows the reaction between magnesium and oxygen to form magnesium oxide. Since oxygen is a diatomic molecule, for every molecule of O₂, there are two oxygen atoms. In the reactants, there are two magnesium atoms from the 2 Mg and two oxygen atoms from the O₂. In the product, each unit of magnesium oxide (MgO) contains one magnesium atom and one oxygen atom, so in 2 MgO, there are two magnesium atoms and two oxygen atoms.
In terms of stoichiometry, the number of atoms in the reactants and products is equal, fulfilling the law of conservation of mass. Therefore, if 3.01 × 10²¹ magnesium atoms react with oxygen, they would produce an equimolar amount of magnesium oxide, ensuring the atoms are conserved.