Question

In the reaction $Mg(s) + 2HCl(aq) \to MgC{l_2}(aq) + {H_2}(g)$, what role does magnesium play?

Answer 1

In the reaction $Mg(s) + 2HCl(aq) \to MgC{l_2}(aq) + {H_2}(g)$ magnesium acts as a reducing agent. A reducing agent also called a reductant or reducer is an element or compound that loses or donates an electron to an electron recipient oxidizing agent in a redox chemical reaction. A reducing agent is thus oxidized when it loses electrons in the redox reaction.

Complete answer:
In the reaction $Mg(s) + 2HCl(aq) \to MgC{l_2}(aq) + {H_2}(g)$ magnesium acts as a reducing agent.
Magnesium metal is being oxidized to magnesium cations, $M{g^{2 + }}$. Hydrogen is being reduced from hydrogen ions, ${H^ + }$, to hydrogen gas, ${H_2}$. So we can presume that the above response is a redox reaction. Consequently, you can say that magnesium is going about as a reducing agent since it reduces hydrogen to hydrogen gas while being oxidized simultaneously. Conversely, hydrochloric acid plays an oxidizing agent's role as it oxidizes magnesium to magnesium cations while being reduced simultaneously.
Magnesium goes from an oxidation state of zero on the reactants' side to an oxidation state of $+ 2$ on the products' side, which means that it is indeed being oxidized. Hydrogen goes from an oxidation state of $+ 1$ on the reactants' side to an oxidation state of $0$ on the products' side, which means that it is reduced. Therefore, you can say that magnesium is acting as a reducing agent because it reduces hydrogen to hydrogen gas while being oxidized in the process.

Note:
Hydrochloric acid, the compound that delivers the hydrogen ions to the reaction, is acting as an oxidizing agent because it oxidizes magnesium to magnesium cations while being reduced in the process. The reaction between magnesium metal and hydrochloric acid is exothermic, because it released energy in the form of heat increase of temperature.