First, we need to determine the number of moles of magnesium Mg and hydrogen gas H2 involved in the reaction. The molar mass of magnesium is 24.31 g/mol. Moles of Mg = mass of Mg / molar mass of MgMoles of Mg = 4.8 g / 24.31 g/molMoles of Mg = 0.197 molAt STP, 1 mole of any gas occupies 22.4 L. Moles of H2 = volume of H2 / molar volume of H2Moles of H2 = 224 mL / 22,400 mL/molMoles of H2 = 0.01 molThe balanced chemical equation for the reaction between magnesium and hydrochloric acid is:Mg + 2HCl MgCl2 + H2From the balanced equation, we can see that 1 mole of Mg reacts with 1 mole of H2. Since we have 0.197 mol of Mg and 0.01 mol of H2, the limiting reactant is H2.Now, we can calculate the enthalpy of ionization of magnesium using the heat released during the reaction -412 kJ/mol and the moles of the limiting reactant H2 .Enthalpy of ionization of Mg = heat released / moles of limiting reactantEnthalpy of ionization of Mg = -412 kJ/mol / 0.01 molEnthalpy of ionization of Mg = -41,200 kJ/molThe enthalpy of ionization of magnesium is -41,200 kJ/mol.