Final answer:
The reactants in the reaction of magnesium with hydrochloric acid to produce magnesium chloride and hydrogen are magnesium and hydrochloric acid, which is option B.
Step-by-step explanation:
The reactants in the chemical reaction where magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen are magnesium and hydrochloric acid. Therefore, the correct answer is B) Magnesium and hydrochloric acid. The balanced chemical equation for this reaction is:
Mg + 2HCl → MgCl₂ + H₂
This reaction is an example of a single replacement reaction where magnesium, a more reactive metal, displaces hydrogen from hydrochloric acid resulting in the formation of magnesium chloride and hydrogen gas. The reaction not only produces a salt, magnesium chloride, but also hydrogen gas, which can be observed as bubbling or fizzing during the reaction.