Q1: J_D factor for mass transfer is a function of Reynolds number. Mass transfer by molecular diffusion from a single drop to surrounding still air is given by

ANS:A - N_sh = 2

The JD (Jakob and Dhanasekharan) factor is used to account for the effect of fluid flow on mass transfer in mass transfer processes. However, the JD factor is not directly related to Reynolds number in the same way as other dimensionless numbers like the Sherwood number (Nsh) for mass transfer, Nusselt number (Nst) for heat transfer, or Schmidt number (Nsc) for mass transfer in forced convection. When mass transfer occurs by molecular diffusion from a single drop to surrounding still air, it is typically characterized by the Sherwood number (Nsh), not the JD factor. The Sherwood number relates the mass transfer rate to the molecular diffusion rate and is a function of the geometry and flow conditions. Given that the diffusion is occurring from a single drop to surrounding still air, the Sherwood number (Nsh) would depend on factors such as the drop diameter, diffusivity of the species, and temperature gradient. The specific value of Nsh would need to be determined based on the specific conditions of the system. Therefore, the correct answer is: none of these.