The correct answer for the question that is being presented above is this one:
Given that:
delta Tb = Kbm Kb H2O = 0.52 degrees C/m
delta Tf = Kfm Kf H2O = 1.86 degrees C/m
We need to know the formula for Molality.
molality = mol solute / kg solvent
We are given the amount of solute in grams
Since amount of solute is given in moles, we have to convert 25 g NaCl to moles. Divide by molar mass.
25 g NaCl / 58.5 g/mol = 0.427 mol
Then, use the formula for molality.
molality = mol solute / kg solvent
= 0.427 / 1
= 0.427 m
Use now the formula to get the boiling point.
delta Tb = Kbm
= (0.52)(0.427)
= 0.22C