Which of the following statements are correct about azeotropic mixtures?

A. They have the same composition in liquid and vapour phases.

B. They can be separated by fractional distillation

C. They are formed at a specific composition.

D. Solutions which show positive deviation from Raoult's law from maximum boiling azeotrope.

E. The azeotrope of ethanol and water is formed by \(80\%\) ethanol and \(20\%\) water.

Choose the correct answer from the options given below:

A and C only

The correct answer is option 3. A and C only.

Let us go through each statement and its explanation:

A. They have the same composition in liquid and vapor phases.

Azeotropic mixtures are characterized by having a constant boiling point. This occurs when the liquid and vapor phases have the same composition. During the process of vaporization (boiling) and condensation, the composition remains constant. This is in contrast to non-azeotropic mixtures, where the composition changes as the components evaporate and condense at different rates.

B. They can be separated by fractional distillation.

Azeotropic mixtures pose a challenge in separation by conventional fractional distillation because the vapor and liquid phases have the same composition. In fractional distillation, the goal is to separate components based on their different boiling points. However, since azeotropic mixtures have a constant boiling point, they cannot be easily separated using conventional fractional distillation.

C. They are formed at a specific composition.

Azeotropic mixtures are indeed formed at specific compositions. These compositions are unique for each azeotropic system and represent the point where the components exhibit maximum miscibility and form a stable azeotrope.

D. Solutions which show positive deviation from Raoult's law form maximum boiling azeotrope.
This statement is not included in the options provided, but it's worth noting that azeotropic mixtures can be categorized as either positive or negative azeotropes. Positive azeotropes occur when the mixture deviates positively from Raoult's law, meaning the vapor pressure of the mixture is higher than predicted by Raoult's law. This deviation leads to the formation of a maximum boiling azeotrope.

E. The azeotrope of ethanol and water is formed by \(80\%\) ethanol and \(20\%\) water.

This statement is incorrect. The composition of an azeotropic mixture is specific and unique to each system. The azeotrope of ethanol and water, for example, is around 95.6% ethanol and 4.4% water. The given composition of \(80\%\) ethanol and \(20\%\) water does not represent the azeotropic composition for this system.

Therefore, considering statements A and C as correct, the correct answer is 3. A and C only