I am new to COMSOL and learning the basics. I am trying to simulate the fluid dynamics in a PFR for 5 % of gas A in nitrogen. So the material is set as nitrogen for the whole domain of the reactor. To make the gas mixture I am using the transport of diluted species module where the number of dependent variables is set as 1. The initial value of conc. is set to 0 and the inflow with the concentration of gas A is set to 5%. After this, I put the laminar flow module with the total input flow rate and other boundary conditions and parameters. Is my model correct? I am confused about the number of dependent variables under the transport of diluted species module. Should it be 1 or 2?