the mole fraction of the solevent in the solution of non volatile is 0.980.the relative lowering of vapour pressure is

Dear Student,

                       We know that Relative lowering of vapour pressure is equal to mole fraction of the solute. Its given by the formula:

                         $\frac{{P_A}^0 - P_A}{{P_A}^0} = X_{solute}$   

       But we have been given mole fraction of the solvent = 0.980 ,
                    
               This implies , mole fraction of the solute = 1-0.980 = 0.02

Hence the relative lowering of vapour pressure is 0.02.

I hope you understood. Keep posting.