Smoker's equation for the calculation of number of equilibrium stages in a continuous binary distillation column is used, when the

• A. relative volatility is close to one (e.g., separation of close boiling isomers).
• B. feed is not at its bubble point.
• C. number of equilibrium stages in only stripping section is to be calculated.
• D. number of equilibrium stages required is likely to be very small.