The chemical equation that will best describe the reaction of magnesium and hydrochloric acid forming magnesium chloride and hydrogen gas is option B. It is expresses as Mg + 2HCl → MgCl2+ H2. In option A, it is not hydrochloric acid that is written instead it is sulfuric acid. In option C. it is manganese instead of magnesium. Lastly, in option D, it is water that is the reactant not hydrochloric acid.