Final answer:
The reaction of 0.5g magnesium with 0.25g oxygen to yield 0.75g of magnesium oxide demonstrates the law of conservation of mass, as the total mass remains constant before and after the reaction.
Step-by-step explanation:
The reaction between magnesium and oxygen to form magnesium oxide is an excellent demonstration of the law of conservation of mass.
According to this fundamental chemistry principle, mass is neither created nor destroyed during a chemical reaction. Therefore, the reactants' mass will always equal the products' mass if no mass is lost to the surroundings.
In the given scenario, 0.5g of magnesium reacts with 0.25g of oxygen to produce 0.75g of magnesium oxide.
This is a perfect example of the law of conservation of mass at play; the total mass of the reacting substances, magnesium and oxygen, at 0.75g, is equal to the mass of the product formed, magnesium oxide.
Thus, this agreement supports the law stating that during a chemical reaction, matter is neither created nor lost.