To answer this question, the relationship between the flow rate (Q10) and cell density depends on the specific context or formula used in the reactor operation, typically based on the rate of growth or biomass production in a bioreactor. However, without additional context, it's difficult to determine which exact formula or parameters are being referred to in this question.
If we consider the options, the most reasonable assumption is that Q10 is a reference to a standard rate or condition for microbial growth, and cell density is typically presented in grams per liter (g/l).
Given that I don't have enough specific information from the problem setup, I would suggest referring to the reactor model or calculations you were using for biomass growth to determine the exact cell density at the flow rate Q10. Based on standard assumptions or your course material, (b) 0.44 g l^-1 might be the correct answer, but you should check the context or any equations provided in your material.