A compound H2X with molar weight of 80g is dissolved in a solvent having density of 0.4 g/ml. Assuming no change in volume upon dissolution, the molality of a 3.2 molar solution is:

Let's assume we have 1 L of the solution.
In this 1L solution, the number of moles of H2X = 3.2 moles (given molarity)
Mass of H2X = number of moles × molar mass = 3.2 moles × 80 g/mol = 256 g
Since the density of the solvent is 0.4 g/ml, the mass of 1L (1000ml) of solvent is 0.4 g/ml × 1000 ml = 400 g
Assuming no volume change on dissolution, the mass of the solution is approximately the sum of the mass of solute and solvent.
Mass of solution ≈ mass of solvent + mass of solute = 400 g + 256 g = 656 g
Molality is defined as the number of moles of solute per kilogram of solvent.
Molality = (moles of H2X) / (mass of solvent in kg) = 3.2 moles / (400 g × (1 kg/1000 g)) = 3.2 moles / 0.4 kg = 8 mol/kg
Therefore, the molality of the solution is 8 mol/kg or 8 m.