If vapour pressure is not a surface phenomena then why on addtion of a non volatile solute the vapour pressure decreases???? Is vapour pressure a bulk phenomena???
Please explain.

The vapour pressure of a solution containing a non volatile solute is actually the the vapour pressure of the solvent in the solution. i.e. V.P of solution = V.P of solvent in the solution Therefore if the mole fraction of the solvent in a solution decreases , the vapour pressure of solution also decreases .....vapour pressure is neither a surface phenomenon nor a bulk phenomenon...

Vapour pressure is neither bulk nor a surface phenomenon but, evaporation is a surface phenomenon. By the addition of non-volatile solute, the upper surface area occupied by solvent decreases due to which it evaporates less and will have comparatively less mole fraction than in pure solvent, because of this its vapour pressure decreases. See the figure, when A+B is present A evaporates less and VP dec.

I think both of these reasons are valid

the same reason is also given in NCERT Niharika and actually this reason confused me