Vapour Pressure of solution can be calculated from the relation: PA∘PA∘−PA=χB=WA/MwAWB/MwB
Here WA=1000g,WA=68.4g,PA∘=0.023atm, MwA=18,MwB=342
Substituting the values, we get 0.0230.023−PA=1000/1868.4/342
or 0.0230.023−PA=342×10068.4×18
or 0.0230.023−PA=0.0036
or 0.023−PA=0.0036×0.023=0.000083 PA=0.023−0.00008=0.02292atm
Vapor pressure of solution =0.02292atm