Which type of chlorine is most commonly used in water disinfection processes?

The option that states "All of the above" is appropriate because each of the chlorine types mentioned plays a role in water disinfection processes, and their usage can depend on various factors such as facility size, application, and local regulations.

Calcium hypochlorite is commonly used in portable water treatment and is popular where chlorine gas might pose a safety risk. It is often found in solid form and can be easier to handle and store.

Sodium hypochlorite, frequently recognized as bleach, is widely used in municipal water systems because it is easy to dispense and has a high availability. It is suitable for both treatment and disinfection in various applications.

Chlorine gas is highly effective due to its strong oxidizing properties and is used in large treatment facilities for water disinfection, though its use requires careful management due to safety concerns.

Since all three types of chlorine can be effectively used for disinfection in different settings, the choice encompassing all options reflects the comprehensive use of chlorine in water treatment and disinfection processes.