Q1: Calculation of mass transfer co-efficient is mostly/normally done using __________ theory.

ANS:B - film

Calculation of mass transfer coefficients is typically done using film theory. Film theory is a common approach used to analyze mass transfer processes, particularly in cases where mass transfer occurs across a phase boundary, such as between a gas and a liquid or between two immiscible liquids. In film theory, it is assumed that a thin film of fluid (often referred to as the "diffusion film" or "boundary layer") adjacent to the interface controls the mass transfer process. The film is assumed to have uniform properties and thickness, and mass transfer occurs through diffusion within this film. While surface renewal theory and penetration theory are also used in certain contexts to analyze mass transfer processes, film theory is the most commonly used approach for calculating mass transfer coefficients, especially in the context of convective mass transfer. Surface renewal theory is more applicable to cases involving turbulent flow and surface renewal, while penetration theory is typically used in cases where the concentration gradient within the bulk fluid is not negligible compared to the concentration at the interface.