Which condition is not satisfied by an ideal solution?

A solution of urea (molar mass $$60 \mathrm{~g} \mathrm{~mol}^{-1}$$ ) boils at $$100.20^{\circ} \mathrm{C}$$ at the atmospheric pressure, if $$K_f$$ and $$K_b$$ for water are 1.86 and $$0.512 \mathrm{~K}$$ $$\mathrm{kg} \mathrm{mol}^{-1}$$ respectively. The freezing point of the solution will be

When difference in boiling points of two liquids is too small, then the separation is carried out by

Which of the following will form an ideal solution?