In McCabe-Thiele method, at infinite reflux ratio

ANS:A - the overhead product is minimum.

In distillation, the "overhead product" refers to the distillate or the product collected from the top of the distillation column. In the context of binary distillation (separation of a mixture into two components), the overhead product is the product containing the more volatile component. When we refer to the "overhead product is minimum" in the context of the McCabe-Thiele method at infinite reflux ratio, it means that the distillate collected is nearly pure with respect to the more volatile component. This occurs because as the reflux ratio increases towards infinity, the amount of reflux (condensed vapor returned to the column) also increases significantly. At infinite reflux ratio:

1. The amount of reflux becomes much larger compared to the amount of distillate.
2. The composition of the vapor in equilibrium with the liquid becomes almost identical to the composition of the liquid.
3. As a result, the distillate becomes almost pure with respect to the more volatile component.

In summary, the statement "overhead product is minimum" means that the distillate collected at infinite reflux ratio is nearly pure, containing only a minimal amount of the less volatile component, while the majority of the more volatile component is returned to the column as reflux.