A solution was made by dissolving 800.0 g of NaOH in 2.00L of water. ?

Molality is moles of solute per 1 kg of solvent.
In the case of water, molality is almost the same as molarity, because 1 liter of water has a mass of right around 1 kg.
The mass of 1 mole of NaOH is 23g + 16g + 1g = 40g, so the 800 grams of NaOH is 20 moles.  Hence you have 20 moles of solute per 2 kg of solvent (water), and the molality is 20/2 = 10 mol/kg....Show more