Which of the following is a chlorine derivative used for disinfection?

• A. Hydrogen peroxide
• B. Calcium hypochlorite
• C. Ozone
• D. Ultraviolet light

Answer: (B)

Chlorine-based disinfection relies on releasing chlorine that forms hypochlorous acid in water, the active agent that inactivates pathogens. Calcium hypochlorite is a chlorine derivative because it supplies available chlorine when dissolved, producing hypochlorous acid for effective disinfection. It’s commonly used in wastewater treatment due to its solid form, ease of storage and handling, and reliable chlorine residual. The other options are not chlorine derivatives: hydrogen peroxide is a different oxidant, ozone is another chlorine-free oxidant, and ultraviolet light disinfects by radiation rather than chemical action.