Mass Transfer
Fenske's equation for determining the minimum number of theoretical stages in distillation column holds good, when the

Mixture (to be separated) shows positive deviation from ideality
Multicomponent distillation is involved
Mixture (to be separated) shows negative deviation from ideality
Relative volatility is reasonably constant

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Mass Transfer
For water-ethanol system, the minimum reflux ratio

Is computed from the intercept of the operating line
Is computed from the slope of the upper operating line that is tangent to the equilibrium curve
Is the optimum reflux ratio
Cannot be computed

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