The maximum yield of H2 from this reaction under the conditions given is 0.3 g.This is a limiting reagent (reactant) question. The yield of hydrogen gas (H2) is determined for both the hydrogen chloride and zinc. The limiting reagent will yield less H2, which is the amount of H2 that can be formed under the given conditions.Start with a balanced equation:Zn + 2HCl --> ZnCl2 + H2You need the molar masses of Zn and HCl. I'm going to round them to whole numbers.HCl: 36 g/molZn: 65 g/molH2: 2 g/molBasic procedure:Determine the moles of the reactant by dividing by its molar mass. Because molar mass is a fraction (g/mol) you can divide by multiplying by its reciprocal. Then multiply by the mole ratio between the reactant and hydrogen gas from the balanced equation, so that mol H2 is in the numerator. Finally, multiply by the molar mass of H2 to get the mass of H2 produced.Yield of H2 from 10 g HCl:10 g HCl x (1 mol HCl)/(36 g HCl) x (1 mol H2)/(2 mol HCl) x (2 g H2)/(1 mol H2) = 0.3 g H2 rounded to one significant figureYield of H2 from 20 g Zn:20 g Zn x (1 mol Zn)/(65 g Zn) x (1 mol H2)/(1 mol Zn) x (2 g H2)/(1 mol H2)= 0.6 mol H2 rounded to one significant figureThe limiting reagent is HCl, which means that the maximum yield of H2 is 0.3 mol H2.