A CM reactor receives influent containing 10.0 mg/L of tracer for 2 h. Then tracer addition is terminated but the flow remains steady. The volume of the reactor is 10 L and the flow rate is 2 L / h. What is the concentration of tracer in the reactor 1 h after tracer addition is terminated? The reactor had an initial concentration of tracer of 1.0 mg/L when tracer addition commenced.