ANS:C -

In the McCabe-Thiele method, which is commonly used for binary distillation, the feed line represents the composition of the feed entering the distillation column. If 𝑓f represents the moles of vapor present per mole of feed, it implies that 𝑓f moles of the feed are vaporized for every mole of feed entering the column. The slope of the feed line in the McCabe-Thiele method is determined by the ratio of the moles of vapor to the moles of liquid in the feed. This ratio, often denoted as 𝐿𝐹𝑉𝐹VF​LF​​, where 𝐿𝐹LF​ is the moles of liquid and 𝑉𝐹VF​ is the moles of vapor in the feed, is equivalent to 1𝑓f1​ for a binary system. So, the slope of the feed line, 𝑚feedmfeed​, is given by: 𝑚feed=1𝑓mfeed​=f1​ Therefore, if 𝑓f represents the moles of vapor present per mole of feed, then the slope of the feed line in the McCabe-Thiele method is 1𝑓f1​.