A. STSK3A

relate the concept of the atom to the conservation of mass; i.e., the number of atoms stays the same as they are rearranged in a chemical reaction; therefore, the total mass before and after the reaction remains the same (e.g., analyze the chemical equation 2Mg(s) + O2(g)→ 2MgO(s) to illustrate the law of conservation of mass by counting the number of atoms of each element)