The products are a salt and hydrogen, MgCl2 and H2.The balanced equation is: Mg + 2HCl -> MgCl2 + H2This is a metal/acid reaction.Mg is a Group 2 metal, so there are two electrons in the outermost shell.Cl is a Group 7 element, so there are seven electrons in the outermost shell.So Mg donates one electron to each Cl atom to form one Mg2+ ion and two Cl- ions (MgCl2).Mg displaces the H in HCl to form MgCl2 because Mg is more reactive than hydrogen, as shown on the reactivity series.