ANS:B - perfectly mixed

The ratio of Murphree plate efficiency to point efficiency is 1 in a perfectly mixed flow model. In a perfectly mixed flow model, it is assumed that the liquid and vapor phases are thoroughly mixed at each tray or stage in the distillation column. This implies that the concentration of the key components is uniform across the entire stage, leading to an equal efficiency for both the Murphree plate efficiency and the point efficiency. Therefore, the correct option is: perfectly mixed.