The incorrect statement about azeotropes is

The components can be separated by fractional distillation.

The correct answer is option 3. The components can be separated by fractional distillation.

Here's why:

1. They are binary mixtures of liquids. This statement can be true or false depending on the specific azeotrope. While most common azeotropes are binary mixtures, some can involve three or more components (ternary, quaternary, etc.).
2. The composition remains the same in liquid and vapour phase, at constant temperature. This statement is true by definition. The unique characteristic of an azeotrope is that boiling doesn't change the composition of the mixture, both phases (liquid and vapor) have the same proportions of components.
3. The components can be separated by fractional distillation. This statement is false. The key point about azeotropes is that simple distillation cannot separate their components. Fractional distillation, which essentially uses repeated distillations, also fails in this case. The reason is that the vaporized mixture retains the same composition as the liquid, making separation through boiling ineffective.
4. They show deviations from Raoult’s law. This statement is true. Raoult's law defines the ideal behavior of liquid mixtures based on their individual vapor pressures. Azeotropes significantly deviate from this ideal behavior, exhibiting either positive or negative deviations depending on the interaction between the components.

Therefore, option 3 is the incorrect statement about azeotropes. They cannot be separated by fractional distillation due to their unique boiling behavior where the vapor and liquid phases maintain the same composition.