Separation of Miscible Liquids A and B

To separate two miscible liquids A and B, which have different boiling points, the most suitable method is Fractional Distillation.

What is Fractional Distillation?
Fractional distillation is a separation technique used to separate two or more miscible liquids based on their boiling points. It is an improved version of simple distillation and is particularly effective when the boiling points of the liquids are close to each other.

Working Principle of Fractional Distillation
Fractional distillation takes advantage of the fact that the liquids in a mixture have different boiling points. The mixture is heated in a fractionating column, which is a long vertical tube with several horizontal condensation plates or trays. As the mixture is heated, the liquid with the lower boiling point vaporizes first. The vapor rises up the fractionating column and comes into contact with the cooler condensation plates. Here, the vapor condenses back into a liquid and then flows back down into the mixture. This process is repeated multiple times as the vapor continues to rise and condense, resulting in the separation of the liquids based on their boiling points.

Why is Fractional Distillation Suitable for Separating A and B?
In the given scenario, liquid A has a lower boiling point (60°C) compared to liquid B (90°C). Therefore, when the mixture is heated during fractional distillation, liquid A will vaporize first. The vapor will rise up the fractionating column and condense on the cooler plates. The condensed liquid A will then flow back down into the mixture, while liquid B remains in the original container. This continuous process allows the separation of the two liquids based on their boiling points.

Other Methods
The other methods mentioned in the options are not suitable for separating two miscible liquids with different boiling points:
- Decantation: Decantation is used to separate a solid from a liquid or two immiscible liquids, and is not effective for separating miscible liquids.
- Distillation: Simple distillation is used to separate a pure liquid from a mixture, but is not suitable for separating miscible liquids with similar boiling points.
- Chromatography: Chromatography is a technique used to separate mixtures based on the differential movement of components through a stationary phase. It is mainly used for separating different components of a mixture, rather than separating miscible liquids.

Therefore, Fractional Distillation is the most appropriate method for separating the miscible liquids A and B in this scenario.