Steady state equimolal counter diffusion is encountered in

ANS:A - separation of a binary mixture by distillation.

The separation of a binary mixture by distillation is a common process used to separate two or more components with different boiling points. Here's an overview of how it works:

1. Introduction to Distillation: Distillation is a separation process that relies on the differences in boiling points of the components in a mixture. It involves heating the mixture to its boiling point to vaporize the more volatile component(s), then condensing the vapor back into liquid form to collect the purified component(s).
2. Batch vs. Continuous Distillation: Distillation can be carried out in either batch or continuous mode. In batch distillation, a finite amount of mixture is heated and separated at once, while in continuous distillation, the mixture is continuously fed into the distillation column, and the purified components are continuously removed.
3. Distillation Column: The key component of a distillation process is the distillation column, which consists of several trays or plates stacked vertically. The column provides a large surface area for the vapor and liquid phases to come into contact and facilitates the separation process.
4. Vapor-Liquid Equilibrium: As the mixture is heated in the distillation column, the more volatile component(s) vaporize and rise through the column, while the less volatile component(s) remain in liquid form and flow downwards. The vapor and liquid phases establish equilibrium conditions, where the compositions of the vapor and liquid phases are determined by the relative volatility of the components.
5. Fractional Distillation: In fractional distillation, the distillation column is equipped with additional features such as packing material or trays with bubble caps to enhance vapor-liquid contact and separation efficiency. This allows for the separation of mixtures with closer boiling points.
6. Condensation and Collection: At the top of the distillation column, the vapor is cooled and condensed back into liquid form. The condensed liquid, known as the distillate, is collected and may undergo further processing or purification steps if necessary. The less volatile components remain in the bottom of the column as the residue.
7. Applications: Distillation is widely used in various industries for the purification of chemicals, separation of petroleum fractions in refineries, production of alcoholic beverages, and many other applications where the separation of components with different boiling points is required.