The question is In the production of a drug having a molecular weight 192, the exit stream from the reactor flows at the rate of 10.3 L/min. The drug concentration is 41.2% (in water) and the specific gravity of the solution is 1.025. Calculate (i) The concentration of the drug in Kg/L in the exit stream (ii) Flow rate in Kg-mol/min. The question I have is When the concentration of the drug is given as 41.2%, is it by mass or by volume? Is there any convention which is followed by engineers in this context? I ask this because in many similar problems, I have the same doubt.