I hope you understand my working: 1) Finding the mol of NH3 to find the mol of (NH4)2SO4 (ammonium sulfate) 2) Mr of (NH4)2SO4 3) Theoretical yield: The actual grams of (NH4)2SO4 produced when reacting 0.514 mol of NH3 to 0.514 mol H2SO4 4) Using formula of (given grams)/(theoretical grams or actual grams) * 100 = 73% 5) Basic algebra