let's start:
16 g NaOH has 84 g of water
moles of NaOH =16/40
=0.4
moles of water =84/18
= 4.667
Total moles = 0.4+4.667
= 5.067
mole fraction of NaOH = 0.4/5.067
= 0.0789
Conclusion:
84 g water will have 0.4 moles of NaOH
1000g water will have [0.4x 1000]/84
= 4.76 moles
This is called molality.
ENJOY :)