ANS:B - Infinity

The reflux ratio at total reflux is infinity. Total reflux refers to the condition in a distillation column where all the condensed vapor from the condenser is returned to the column as reflux. In this scenario, no distillate product is withdrawn from the column. The reflux ratio (𝑅𝑅RR) is defined as the ratio of the reflux flow rate to the distillate flow rate (𝐿/𝐷L/D). When there is no distillate withdrawn (total reflux), the distillate flow rate (𝐷D) becomes zero, making the reflux ratio undefined. Mathematically, 𝑅𝑅=𝐿𝐷RR=DL​, and when 𝐷=0D=0, 𝑅𝑅=𝐿0RR=0L​, which is infinity. So, at total reflux, the reflux ratio is infinity.