ANS:C - extractive

In case of extractive distillation, a solvent is added to alter the relative volatility of the mixture to be separated. In extractive distillation, a third component (the solvent) is introduced into the system to improve the separation efficiency by modifying the relative volatility of the components in the mixture. The solvent selectively interacts with one or more components of the mixture, thereby changing their vapor-liquid equilibrium behavior. By adding the solvent, the relative volatility between the components of interest can be increased or decreased, making it easier to separate them through distillation. This process is particularly useful when the components of the mixture have similar boiling points or form azeotropic mixtures that are difficult to separate by conventional distillation methods. Therefore, in extractive distillation, the addition of a solvent plays a crucial role in altering the relative volatility of the components, leading to enhanced separation efficiency.