According to the law of conservation of mass, the total mass of the reactants equals the total mass of the products in a chemical reaction.
The reaction is: \[ 2Hg + O_2 \rightarrow 2HgO \]
Since the total mass of the product (mercuric oxide, HgO) is 433.2 grams, the total mass of the reactants (mercury and oxygen) must also be 433.2 grams.
Therefore, the total mass of the mercury and oxygen on the reactants side of the equation is:
433.2 grams