ANS:A - individual mass transfer co-efficient (M.T.C.) in gaseous system.

The wetted wall tower is used to determine the individual mass transfer coefficients (M.T.C.) in a gaseous system. In a wetted wall tower, a liquid film flows down the walls of a vertical column while gas flows upward through the column. This setup allows for controlled conditions in which mass transfer occurs between the gas phase and the liquid film. By measuring the concentration profiles of the gas and liquid phases along the height of the tower, one can determine the individual mass transfer coefficients of the gas phase components. This information is valuable for understanding the rates at which different components are transferred between the gas and liquid phases in various chemical and engineering processes, such as absorption, desorption, and distillation.