Which statement best explains how chemical equations demonstrate the Law of Conservation of Mass with respect to O_2 and CO_2 in a reaction?

• A. The total amount of O_2 and CO_2 is always less after the reaction because some mass is lost as energy.
• B. The number of oxygen atoms in the reactants (O_2) equals the number of oxygen atoms in the products (CO_2), showing that mass is conserved.
• C. The equations indicate that O_2 and CO_2 are interchangeable, so their amounts can change freely.
• D. Chemical equations show that O_2 is always completely converted to CO_2, so the total mass increases.

Answer: (B)

Verified step by step guidance

1. Understand the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction; it can only be rearranged.
2. Recognize that chemical equations represent this law by showing the same number of each type of atom on both sides of the equation (reactants and products).
3. Focus on the oxygen atoms in the reaction: count the number of oxygen atoms in the reactant molecules (O_2) and compare it to the number of oxygen atoms in the product molecules (CO_2).
4. Note that the total number of oxygen atoms remains constant before and after the reaction, demonstrating that no oxygen atoms are lost or gained, just rearranged.
5. Conclude that this equality in the number of oxygen atoms illustrates how chemical equations uphold the Law of Conservation of Mass.