Here's why:

* Zero B purification refers to a process that removes both bacteria and viruses.

* Chlorine is a highly effective disinfectant that kills both bacteria and viruses. It's a common and inexpensive method for water purification.

* Other halogens like bromine and iodine can also be used for disinfection, but chlorine is the most widely used due to its cost-effectiveness and effectiveness.

It's important to note that the "zero B" term might not always be accurate. While chlorine can eliminate most harmful microorganisms, it may not completely eliminate all viruses and bacteria. The effectiveness of chlorine disinfection depends on factors like water quality, contact time, and chlorine concentration.