The balanced equation for the reaction between magnesium (Mg) and hydrochloric acid (HCl) is:

Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

In this reaction, solid magnesium (Mg) reacts with hydrochloric acid (HCl) in an aqueous solution (aq) to produce magnesium chloride (MgCl2) in an aqueous solution (aq) and hydrogen gas (H2) as a product.