On a distillation plate, which change most directly increases liquid-side resistance to mass transfer and thus lowers plate efficiency?

Introduction / Context:
Tray efficiency depends on vapor-liquid interfacial area and the resistances to mass transfer on the gas and liquid sides. Understanding which variables worsen liquid-side resistance helps diagnose low efficiency and guides solvent and operating condition choices.

Given Data / Assumptions:

• Conventional tray column (distillation as the main context).
• Focus is the effect on liquid-film resistance.
• No flooding, weeping, or foaming issues assumed.

Concept / Approach:
Liquid-film mass-transfer coefficients generally decrease as viscosity rises, because higher viscosity dampens turbulence and reduces diffusivity. Hence, higher viscosity increases the liquid-side resistance, lowering stage efficiency. By contrast, higher relative volatility improves separation driving force in distillation, not resistance. Gas solubility pertains more to absorption/stripping gas-side phenomena than to liquid-side resistance on distillation trays.

Step-by-Step Solution:
Identify the direct influencer of liquid film properties: viscosity.Recognize that increased viscosity → lower liquid-side mass-transfer coefficient.Infer lower Murphree/overall efficiency for the same contacting time and area.

Verification / Alternative check:
Correlations for kL often show inverse dependence on viscosity (e.g., via dimensionless groups like Sc and Re), confirming the trend.

Why Other Options Are Wrong:
Higher relative volatility increases thermodynamic driving force; it does not increase resistance.Lower gas solubility affects gas-side transfer in absorbers, not directly the liquid-film resistance on trays in distillation.

Common Pitfalls:
Blaming tray design alone when liquid properties (viscosity, foaming) limit transfer; ignoring temperature changes that reduce viscosity and improve efficiency.

Final Answer:
An increase in liquid viscosity