In your lab, the mass of your product is less than the mass of your reactants. You recall that atoms are not created or destroyed in a chemical reaction, they are just rearranged from the reactants to form the products. You are afraid you have misunderstood something, so you ask your teacher for some help. She reminds you that if a chemical reaction is completed in a closed system then the mass will remain constant. But if the chemical reaction happens in an open system the mass may appear to change. What can account for this apparent difference?

A The chemical reaction is in a closed system and the reactants
are all solid, while the products are liquid.

B The chemical reaction is in an open system and the reactants
are all liquid, while the products are solid.

C The chemical reaction is in an open system and a gas is being
released into the atmosphere.

D The chemical reaction is in a closed system and a gas is being
used as a reactant.