The vapour pressure of a solution (P) and the vapour pressure of the solvent `(P^(@))` are related to each others as `(x_(1)` is the mole fraction of solvent)

If P^(@) the vapour pressure of a pure solvent and P is the vapour pressure of the solution prepared by dissolving a non volatile solute in it. The mole fraction of the solvent X_(A) is given by:

The vapour pressure of a solution having solid as solute and liquid as solvent is:

The vapour pressure of solvent is 20 torr, while that of its dilute solution is 17 torr , the mole-fraction of the solvent is