d
\(\frac{{{P^ \circ }\, - \,\,{P_s}}}{{{P_s}}}\,\, = \,\,\frac{{{W_{solute}}\, \times \,\,{{(Mol.wt.)}_{solvent}}}}{{{{(Mol.wt.)}_{solute}}\,\, \times \,{W_{solvent}}}}\)
\(\frac{{17.5\,\, - \,\,{P_s}}}{{{P_s}}}\,\, = \,\,\,\frac{{18\,\, \times \,\,18}}{{180\,\, \times \,\,178.2}}\,\,\, \Rightarrow \,\,{P_s}\,\, = \,\,17.325\,\,mm\,\,Hg\)