Dear Student,
According to the given balanced equation, the stiochiometry suggests that 1 mol of CaCO3 requires to evolve 1 mol of CO2.
But in the reaction when 1 mol of CaCO3 reacts with 2 mol of HCl it give 1 mol of CO2. Or can be said as that 100 g of CaCO3 reacts with 73 g of HCl to produce 44 g of CO2.
So, 20 g of CaCO3 will react with
So the limiting reagent is CaCO3, and the number of moles of CaCO3 consumed will be 20/100 = 0.2 moles
and according stiochiometry 0.2 mol of CO2 will be produced = 0.2 x 44 = 8.8 g
So, the amount of CO2 will be produced is 8.8 g
Regards.