Final answer:
The objective of adding chlorine to water is to sanitize the water and prevent algae growth, corresponding to both A and C options. Chlorine's role as a disinfectant is essential for making water safe for consumption and it must be carefully measured to avoid health risks.
Step-by-step explanation:
The objective of adding chlorine to water is primarily to sanitize the water and to prevent growth of algae; therefore, the correct answer is D) Both A and C above. Chlorine is widely used as a disinfectant because it effectively eliminates bacteria and other harmful organisms, making the water safe for human consumption. However, the process must be carefully managed to ensure that the amount of chlorine is sufficient to disinfect but not so much as to pose a hazard to human health or aquatic life. After chlorine has completed its disinfection, it may be necessary to neutralize it with other chemicals so that it does not harm marine organisms. Chlorine's effectiveness against pathogens like Escherichia coli makes it a popular choice for water treatment. While filtration and flocculation are important in removing suspended particles and purifying water, they are not directly related to chlorine's role in water treatment.