ANS:A - McCabe-Thiele method

The method that assumes constant molal vaporization and overflow is the McCabe-Thiele method. The McCabe-Thiele method is a graphical technique used for the design and analysis of binary distillation columns. It assumes that the relative volatility of the components remains constant throughout the column, as well as constant molal vaporization and liquid overflow. In the McCabe-Thiele method, the number of theoretical stages required for separation is determined based on the equilibrium relationship between the vapor and liquid phases, and the operating lines representing material balances for the distillation column. The method provides insights into the required number of stages, reflux ratio, and feed conditions for achieving the desired separation efficiency. The other methods mentioned:

• Ponchan-Savarit method: A graphical method for analyzing absorption processes in packed columns.
• Enthalpy concentration method: A method used for analyzing multi-component distillation systems based on energy balances.
• Plate absorption column: A type of absorption column used for gas-liquid contact in separation processes.