Solution:Concept- The amount of dissolved oxygen in water varies. Additionally, it might come from the atmosphere or be produced as a result of photosynthesis by aquatic plants.
The dissolved oxygen is what allows aquatic life to survive. BOD is a crucial sign of water pollution because it measures the amount of dissolved oxygen that aquatic life needs.
The BOD will increase with water contamination, indicating a greater level of water pollution. The application of this property in sewage treatment plants is widespread. Aerobic bacteria are added to the raw sewage water, where they degrade the organic contaminants and aid in the decomposition of the sewage.
Hence, the correct answer is option 1 - Reduce BOD.