ANS:A - 1.2 to 1.5

In distillation, the reflux ratio is the ratio of the liquid returned to the top of the column to the liquid removed from the bottom of the column. The minimum reflux ratio (Rm) represents the lowest ratio at which the separation is feasible. The optimum reflux ratio is typically higher than the minimum reflux ratio and is often determined through iterative calculations or graphical methods to achieve desired separation efficiency. Commonly, the optimum reflux ratio can be around 1.2 to 1.5 times the minimum reflux ratio. So, the correct answer is: 1.2 to 1.5 times Rm.