ANS:B - decreases

In batch distillation with constant reflux, overhead product composition may increase or decrease, depending on the system. Explanation:

1. Batch Distillation:
   • In batch distillation, a finite quantity of feed mixture is loaded into the distillation apparatus, and the separation process occurs in a batch mode.
   • The distillation process involves heating the feed mixture to vaporize its components, followed by condensation and collection of the overhead (vapor) and bottoms (liquid) products.
2. Constant Reflux:
   • Reflux is the portion of the overhead vapor that is condensed and returned to the distillation column.
   • Constant reflux refers to maintaining a constant reflux ratio throughout the distillation process, where a fixed fraction of the overhead vapor is refluxed back into the column.
3. Overhead Product Composition:
   • The composition of the overhead product (vapor) in batch distillation can vary over time due to changes in the composition of the remaining liquid in the distillation vessel.
   • Initially, the overhead product composition may be rich in the more volatile components of the feed mixture, resulting in a higher concentration of these components in the collected vapor.
   • As the distillation progresses and the concentration of the more volatile components in the remaining liquid decreases, the composition of the overhead product may change accordingly.
   • Therefore, the overhead product composition may increase or decrease with time, depending on the relative volatility of the components in the feed mixture and their distribution between the vapor and liquid phases during the distillation process.

In summary, in batch distillation with constant reflux, the overhead product composition may vary over time depending on the system parameters such as the relative volatility of the components and their distribution between the vapor and liquid phases. Therefore, the correct statement is: "may increase or decrease, depending on the system."