Q1: Mass transfer co-efficient is directly proportional to D_AB^0.5, according to __________ theory.

ANS:A - penetration

The theory stating that the mass transfer coefficient is directly proportional to 𝐷𝐴𝐵0.5DAB0.5​ is known as the penetration theory. The penetration theory is a mass transfer theory that describes the process of mass transfer across a boundary layer. It suggests that the rate of mass transfer is proportional to the square root of the diffusivity of the diffusing species in the bulk fluid. Therefore, the correct answer is: penetration theory.