Question

Na2CO3 reacts with H2SO4 to give respective salt water and carbon dioxide. Calculate the mass of pure salt formed when 300 g of Na2CO3 of 80% purity reacts with H2SO4

Answer 1

You need a comma in the question between salt and water. It is salt, water and CO2 (not salt water and CO2).
Na2CO3 + H2SO4 ==> Na2SO4 + H2O + CO2
mols Na2CO3 if pure = grams/molar mass = 300/142 = about 2 but that's an estimate.
It's only 80% so 2 x 0.80 = about 1.6 g Na2SO4 actually there.
Convert mols Na2CO3 to mols Na2SO4. Then
g Na2SO4 = mols Na2SO4 x molar mass Na2CO3

Answer 2

321.51gm