ANS:A - D

According to the film theory of mass transfer, the mass transfer coefficient (𝑘k) is proportional to the square root of the molecular diffusivity (𝐷D). So, the correct option is 𝐷0.5D0.5. The film theory of mass transfer suggests that the mass transfer rate across a fluid film boundary layer is primarily controlled by molecular diffusion. The mass transfer coefficient 𝑘k is proportional to the square root of the molecular diffusivity 𝐷D, and it can be expressed as: 𝑘∝𝐷k∝D​ This relationship implies that as the molecular diffusivity increases, the mass transfer coefficient also increases, leading to a higher rate of mass transfer across the boundary layer.