The correct answer is option 'A', the Schmidt number.

Explanation:
The Schmidt number (Sc) is a dimensionless quantity that relates the momentum diffusivity (kinematic viscosity) of a fluid to its mass diffusivity (diffusion coefficient). It is defined as the ratio of the momentum diffusivity to the mass diffusivity.

In fluid mechanics and heat transfer, the velocity profile describes how the velocity of a fluid varies across a flow field, while the concentration profile describes how the concentration of a solute or species varies across the same flow field. These profiles are important in many chemical engineering processes, such as mixing, reaction kinetics, and mass transfer.

The velocity profile and concentration profile are linked through the concept of mass transfer. Mass transfer refers to the movement of a solute from an area of high concentration to an area of low concentration, driven by a concentration gradient. This movement occurs due to the random motion of molecules, known as diffusion.

The rate of mass transfer is influenced by the velocity of the fluid (which affects the convective transport of the solute) and the concentration gradient (which affects the diffusive transport of the solute). The Schmidt number quantifies the relative importance of these two transport mechanisms.

In general, a higher Schmidt number indicates a greater dominance of convective transport over diffusive transport. This means that the velocity profile has a stronger influence on the concentration profile. On the other hand, a lower Schmidt number indicates a greater dominance of diffusive transport over convective transport, with the concentration profile being more affected by the diffusive transport.

Therefore, the Schmidt number acts as a connecting link between the velocity and concentration profiles, indicating the relative importance of convective and diffusive transport in mass transfer processes.

To summarize, the Schmidt number is the parameter that connects the velocity and concentration profiles in mass transfer processes, indicating the relative importance of convective and diffusive transport.