The boiling point of a solvent containing non volatile solute :

Explanation

It states that the relative lowering of vcapour pressure is equal to mole fraction of solute which is non volatile. Mathematically - `(P_(A)^(O)-P)/(P_(A)^(O))=X_(B)`
Non-ideal solutions show positive when the partial pressure of each component and hte resultant total pressure are greater than the pressure expected on the basic of Raoult.s law.