Why is chlorine used in pool sanitation?

Chlorine is primarily used in pool sanitation because it effectively kills harmful bacteria and germs present in the water. It acts as a powerful disinfectant, which is crucial for maintaining safe and hygienic swimming conditions. When chlorine is added to pool water, it interacts with microorganisms and disrupts their cellular processes, thereby eliminating pathogens that could pose health risks to swimmers, such as E.coli or other waterborne illnesses.

While the other options mention aspects relevant to pool maintenance, none address the primary purpose of chlorine in a direct way. Improving appearance pertains more to clarity and balance of water, adjusting pH levels is important for overall water chemistry, and enhancing smell is not a goal of chlorine use; rather, it's a sanitizer that can often produce an odor itself if not managed correctly. Thus, the emphasis on chlorine’s role as a bactericide is vital for ensuring swimmer safety and promoting public health in aquatic facilities.