ANS:D - high reflux ratio

For a binary mixture with low relative volatility, continuous rectification to obtain pure products typically requires high reflux ratio. Here's why:

1. Low Relative Volatility: A low relative volatility means that there is a small difference in the vapor pressures of the components in the binary mixture. This implies that the components have similar tendencies to vaporize, making it challenging to separate them efficiently.
2. Continuous Rectification: Continuous rectification, also known as continuous distillation, is a process where the feed mixture is continuously introduced into the distillation column, and the separated products are continuously withdrawn from the column. In continuous distillation, maintaining a concentration gradient along the column is crucial for effective separation.
3. High Reflux Ratio: A high reflux ratio means that a significant portion of the condensed vapor (reflux) is returned to the column as liquid. This increases the liquid holdup in the column and promotes better separation by providing more stages for equilibrium to occur. In the case of a low relative volatility mixture, a high reflux ratio is necessary to enhance the concentration gradient along the column, allowing for better separation of the components.