If the desired dosage is 6.4 mg/l and the chlorine demand is 3.1 mg/l, what is the residual chlorine level?

To determine the residual chlorine level, we use the formula:

Residual Chlorine = Desired Dosage - Chlorine Demand.

Given that the desired dosage of chlorine is 6.4 mg/l and the chlorine demand is 3.1 mg/l, we can subtract the chlorine demand from the desired dosage:

Residual Chlorine = 6.4 mg/l - 3.1 mg/l = 3.3 mg/l.

Thus, the correct value for the residual chlorine level is 3.3 mg/l. This means that after accounting for the chlorine that is consumed in the process (the chlorine demand), the effective residual chlorine available in the water is 3.3 mg/l, confirming the choice as accurate. Understanding how chlorine demand affects the residual chlorine level is essential for ensuring adequate disinfection in water treatment processes.