Final answer:
The law of conservation of mass requires that atoms are balanced on both sides of a chemical equation. The provided equation (C + O2 -> 2CO) is unbalanced; the correct balanced equation is 2C + O2 -> 2CO, which upholds the law of conservation of mass.
Step-by-step explanation:
The law of conservation of mass states that in any chemical reaction, the mass of the substances that react equals the mass of the products formed. When balancing the chemical equation C + O2 -> 2CO, we observe that the equation does not demonstrate the law of conservation of mass because the atoms are not balanced. To correct this, the balanced chemical equation should be 2C + O2 -> 2CO, indicating that two carbon atoms react with one molecule of oxygen to form two molecules of carbon monoxide.
By proving that the law of conservation of mass is obeyed, we ensure the number of atoms of each element is the same on both the reactant and product sides of the equation. Hence, two atoms of carbon and two atoms of oxygen are present before and after the reaction. This demonstrates that the mass before and after the reaction is conserved, as there is no loss or gain of atoms.