Graphically prove that `T_(b)` is greater than `T_(b) ^(@).`

Explanation

(i) The vapour pressure of the solution increases with increase in temperature. The variation of vapoup pressure with respect to temperature of pure water is given by the curv-A.
(ii) At `100^(@)C,` the vapour pressure of water is equal to 1 atm. Hence, the boiling point of water is `100^(@)C(T _(b) ^(@)).`
(iii) When a solute is added to water, the vapour pressure of the reslultant solution is lowered. The variation of vapour pressure with respect to temperature for the solution is given by curve-B.
(iv) From the graph, it is evident that the vapour pressure of the solution is equal to 1 atm. pressure at the temperature `T _(b)` which is greater than `T_(b) ^(@).` The difference between these two temperatures `(T_(b)-T_(b)^(@))` gives the evavation of boiling point.
`DeltaT_(b) = T_(b) - T_(b) ^(@).`