Two liquids are mixed together to form a mixture which boils at same temperature and their boiling point is higher than the boiling point of either of them so they shows.

If force of attraction between A and B (solvents) is higher than that between A and A or B and B, then there is decrease in vaporization. Thus, higher temperature (i.e. boiling point) is required to convert liquids into vapour state. This is a case of negative deviation from Raoult's law.