a pressure of 96.5Kpa is exerted by a mixture of nitrogen gas and water vapor in a equilibrium with liquid water at 18 degree celcius , what is the partial pressure exerted by the nitrogen gas?
Look up the vapor pressure of H2O at 18 C. This is the partial pressure of H2O at that T.
Ptotal = pN2 + pH2O.
You know Ptotal and pH2O. Solve for pN2.