The diagram given below represents the vapour pressure and mole fraction of an ideal solution of component 1 and 2. Answer the following questions. What does lines I, II and III indicate?

These lines (I and II) pass through the points for which x1 and x2 are equal to unity. The plot (line III) of ptotal versus x2 is linear. The plot of vapour pressure and mole fraction of an ideal solution at constant temperature i.e. the dashed lines I and II represent the partial pressure of the components. The total vapour pressure is given by line marked III.