Now....."Molality"Molality == "Moles of solute"/"Kilograms of solvent."Moles of soluteKilograms of solvent.
And our NaOH(aq)NaOH(aq) solution is 3.0*"molal"3.0⋅molal, i.e. 3.0*mol*kg^-13.0⋅mol⋅kg−1
Now chi_(NaOH)="Moles of NaOH"/"Moles of NaOH + moles of water"χNaOH=Moles of NaOHMoles of NaOH + moles of water
=(3.0*mol)/(3.0*mol+(1000*g)/(18.01*g*mol^-1))=3.0⋅mol3.0⋅mol+1000⋅g18.01⋅g⋅mol−1
=(3.0*mol)/(3.0*mol+55.52*mol)=0.0513=3.0⋅mol3.0⋅mol+55.52⋅mol=0.0513