First off, we must build the reactants. We know that solid magnesium reacts with aqueous hydrochloric acid. This gives us Mg(s) + HCl(aq). Now, we need to find the products. We know that aqueous magnesium chloride and hydrogen gas are produced. This is represented by MgCl2(aq) + H2(g). Now, we must simply put together the products and reactants of our single replacement reaction. Mg(s) + HCl(aq) --> MgCl2(aq) + H2(g). The question says not to balance, so that is our answer.
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