Which test measures the effectiveness of chlorine disinfection?

The residual chlorine test is the correct choice for measuring the effectiveness of chlorine disinfection. This test determines the amount of free or combined chlorine remaining in the water after it has undergone the disinfection process. The presence of residual chlorine indicates that chlorine is still active in the water and available to kill any remaining pathogens. It reflects the sufficiency of the chlorine dosage and the overall effectiveness of the disinfection treatment.

In contrast, the pH test measures the acidity or alkalinity of the water, which can impact the effectiveness of chlorine but does not directly indicate how much chlorine is actually present or how well it has disinfected the water. The turbidity test assesses the clarity of water and indicates the presence of suspended particles that could shield microorganisms from chlorine. Lastly, the color test measures the water's appearance and may indicate some contamination but does not provide relevant information about chlorine effectiveness in disinfection. Thus, selecting the residual chlorine test provides a direct assessment of disinfection effectiveness.