Final answer:
The oxidation numbers in the reaction Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) are 0 for Mg(s), +2 for Mg in MgCl2, +1 for H in HCl, -1 for Cl in HCl, and 0 for H in H2(g).
Step-by-step explanation:
The oxidation numbers of the atoms in the reaction Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) are as follows: For elemental magnesium (Mg) in its solid state, the oxidation number is 0. In the compound magnesium chloride (MgCl2), magnesium (Mg) takes on an oxidation number of +2 due to it being a Group 2 metal and having lost two electrons. Each chlorine atom (Cl) in hydrochloric acid (HCl) and in magnesium chloride (MgCl2) has an oxidation number of -1. This is consistent with chlorine being more electronegative and typically taking one electron to fill its outer shell.
Hydrogen (H) in hydrochloric acid (HCl) has an oxidation number of +1, as hydrogen is less electronegative than chlorine and loses an electron. However, in H2 gas, the hydrogen is in its elemental form and thus has an oxidation number of 0. To summarize the oxidation states: In Mg(s), the oxidation number for magnesium (Mg) is 0. In HCl, the oxidation number for hydrogen (H) is +1, and for chlorine (Cl) is -1. In MgCl2(aq), the oxidation number for magnesium (Mg) is +2, and for each chlorine (Cl) atom is -1. In H2(g), the oxidation number for hydrogen (H) is 0.