What does hydrochloric acid produce when reacted with magnesium?

When hydrochloric acid (HCl) reacts with magnesium (Mg), the primary reaction taking place is the formation of magnesium chloride (MgCl₂) and hydrogen gas (H₂). The balanced chemical equation for this reaction can be represented as:

[ \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 ]

This shows that magnesium displaces hydrogen from hydrochloric acid, resulting in the production of magnesium chloride, a salt, and hydrogen gas.

Magnesium chloride is soluble in water and, since the reaction produces hydrogen, you would observe the evolution of gas bubbles during the reaction. This aligns perfectly with the correct choice as it indicates both products formed from the reaction: magnesium chloride and hydrogen. Hence, the correct answer is indeed magnesium chloride and hydrogen.