ANS:C - Never

The efficiency of a plate in a distillation tower cannot exceed 100%. Explanation:

• The efficiency of a plate in a distillation tower refers to its ability to achieve separation between the components in the vapor and liquid phases as they interact on the plate.
• Efficiency is typically expressed as a percentage, where 100% efficiency would mean perfect separation with no mixing of the vapor and liquid phases.
• In practical terms, achieving 100% efficiency is not feasible due to factors such as vapor-liquid equilibrium limitations, mass transfer resistances, and non-ideal behavior.
• While it's theoretically possible to achieve higher efficiencies by increasing the number of plates (theoretical trays), in actual operations, there are diminishing returns as the number of plates increases, and 100% efficiency is not attainable.
• The concept of efficiency exceeding 100% is not meaningful in the context of distillation towers, as it would imply that more separation is achieved than what is theoretically possible, which violates thermodynamic principles.
• Therefore, the correct answer is "Normally not; but is possible if an infinite number of plates are put." This statement acknowledges that while extremely high efficiencies can be approached with a large number of theoretical trays, surpassing 100% efficiency is not realistic or meaningful in practical distillation operations.