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Question:

8g of NaOH is dissolved in 18g of H2O. Mole fraction of NaOH in solution and molality (in mol/kg) of the solutions respectively are:

0.167,11.11

0.2,22.20

0.2,11.11

0.167,22.20

Solution:

8g NaOH, mol of NaOH = 8/40 = 0.2 mol
18g of H2O, mol of H2O = 18/18 = 1 mol
∴ XNaOH = 0.2/1.2 = 0.167
Molality = 0.2 × 1000/18 = 11.11 m.
Hence, the correct option is A