The density of 20% (w/w) aqueous NaOH solution is 1.20 g.mL–1. What is the mole fraction of water ?(molar mass of NaOH = 40g.mol–1)

For the given solution,     d=1.2 g/ml                                                            Wsolute= 20g   ;    Wsol.= 100gm                     Wsolvent= (100 - 20) =80gm