From ideal gas eqn. we get,
PV = nRT
n = (778.6*240)/(760*1000*300*0.0821) = 0.00998 moles of CO2.
Now let x be the weight of Na2CO3 present in the mixture.
Then the reaction is:
Na2CO3 + 2HCl ==========>>>>>>. 2NaCl + CO2 + H2O
moles of Na2CO3 => moles of CO2 => 0.00998
mass of Na2CO3 => 0.00998*106 = 1.055 gms which is exceeding th 1 gm and therfore cannot be possible.
U need toc heck the qstn. or the reaction would not feasible.