ANS:B - infinite

The fixed cost of a distillation column at the minimum reflux ratio is not necessarily minimum, infinite, or optimum. The fixed cost of a distillation column typically depends on various factors such as its size, materials, design complexity, construction methods, and other engineering considerations. The minimum reflux ratio refers to the lowest ratio of reflux to distillate that still ensures separation of the desired components. While operating at the minimum reflux ratio might reduce operating costs (such as energy consumption), the fixed cost of the column itself would depend on the specific requirements of the process and the design specifications needed to achieve separation objectives. So, the correct answer is: none of these.