Explain the terms ideal and non-ideal solutions in the light of forces of interactions operating between molecules in liquid solutions.

△_mixH = 0, △_mix V= 0 
A—B interactions.-- A—A interactions and B—B interactions.

Non-ideal solutions: When a solution does not obey Raoult's law over the entire range of concentration, it is called non-ideal solution. 

Positive deviations: Vapour pressure of such solutions shows higher value than the predicted value. 

△_mix^H = +ve        △_mix^V = +ve 

A—B interactions

Negative deviation: Vapour pressure of such solutions shows lower value than expected. 

△_mixH = —ve          △_mixV = —ve

 A—B interactions > A—A and B—B interactions. 

Refer to page 45 of NCERT textbook for Class XII.