The amount of dissolved oxygen in water becomes lowest at what time of the day?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. In the dawn.
The amount of dissolved oxygen in water becomes lowest in the dawn. This happens because, throughout the night, photosynthesis ceases due to lack of sunlight, while respiration by aquatic plants, animals, and microorganisms continues, consuming oxygen. Since no new oxygen is produced during the night, its levels steadily decline. By dawn, just before sunlight triggers photosynthesis again, the oxygen concentration in the water reaches its minimum point. This natural cycle is important in aquatic ecosystems, and consistently low oxygen levels at dawn can be a sign of poor water quality or excessive organic matter in the water body.