\(a.n_{SO_2}=\dfrac{6,72}{22,4}=0,3\left(mol\right)\\ Ba\left(OH\right)_2+SO_2\rightarrow BaSO_3\downarrow+H_2O\\ n_{BaSO_3}=n_{Ba\left(OH\right)_2}=n_{SO_2}=0,3\left(mol\right)\\ m_{BaSO_3}=217.0,3=65,1\left(g\right)\\ b.C_{MddBa\left(OH\right)_2}=\dfrac{0,3}{0,2}=1,5\left(M\right)\)