From the reaction MgCO3 + 2HCl → MgCl2 + CO2 + H2O
There should be one limiting reagent.
To find the limiting reagent, divide the given moles by stoichiometric coefficient.
∴ moles of CO2 produced = 3 moles
∴ volumes of CO2 produced at S.T.P, = 3 x 22.4 = 67.2 L