5 g of Na₂SO₄ was dissolved in x g of H₂O. The change in freezing point was found to be
3.82^oC. If Na₂SO₄ is 81.5% ionised,
the value of x
(K_f for water=1.86^oC kg mol^−1) is approximately :
(molar mass of S = 32 g mol^−1 and that of Na = 23 g mol^−1)