ANS:A - film

The statement "Mass transfer coefficient is directly proportional to 𝐷𝐴𝐵DAB​" is associated with the film theory. In the film theory of mass transfer, it is assumed that mass transfer occurs through a stagnant film of liquid adjacent to the interface between two phases (such as gas and liquid). According to this theory, the rate of mass transfer is proportional to the diffusion coefficient (𝐷𝐴𝐵DAB​) of the solute in the stagnant film. Therefore, as the diffusion coefficient increases, the mass transfer coefficient also increases, leading to higher rates of mass transfer.