The correct option is B 71 %
Na2SO4+BaCl2→BaSO4↓+2NaCl
Moles of BaSO4=given massmolar mass=11.65233=0.05 mol
According to the reaction, 1 mole of BaSO4 precipitate is obtained from 1 mole of Na2SO4
0.05 moles of BaSO4 will be produced by 0.05 mole of Na2SO4
Amount of pure Na2SO4 required = 0.05 mol ×142 (gmol)=7.1 g
Percentage purity=mass of pure compound in sampletotal mass of impure sample×100 =7.110×100
=71%