ANS:C - momentum diffusivity/mass diffusivity.

In physical terms, the Schmidt number (𝑆𝑐Sc) represents the ratio of momentum diffusivity to mass diffusivity in a fluid. Mathematically, it is defined as: 𝑆𝑐=Momentum diffusivityMass diffusivitySc=Mass diffusivityMomentum diffusivity​ or 𝑆𝑐=𝜈𝐷Sc=Dν​ where:

• 𝜈ν is the kinematic viscosity of the fluid,
• 𝐷D is the mass diffusivity of the species undergoing mass transfer.

The Schmidt number is a dimensionless quantity used in fluid dynamics and mass transfer to characterize the relative importance of momentum and mass transport in a fluid. It provides information about how rapidly momentum and mass are transported through a fluid compared to each other. A low Schmidt number indicates that mass transfer occurs more rapidly than momentum transfer, meaning that the fluid has a high capacity for mass transfer relative to momentum transfer. Conversely, a high Schmidt number suggests that momentum transfer dominates over mass transfer, implying that the fluid has a high capacity for momentum transfer relative to mass transfer. In summary, the Schmidt number quantifies the relative importance of momentum and mass transport in a fluid and is particularly relevant in situations where both momentum and mass transfer occur simultaneously, such as in fluid flow with mass transfer or in convective heat transfer with species diffusion.