The correct answer is: A. Maximum at noon.
Dissolved oxygen (DO) is the amount of oxygen that is dissolved in water. It is essential for aquatic life, as it is used in respiration. DO levels can vary depending on a number of factors, including temperature, salinity, and the presence of pollutants.
In general, DO levels are highest during the day and lowest at night. This is because photosynthesis, which produces oxygen, occurs during the day. At night, respiration, which consumes oxygen, occurs.
In addition, DO levels can be affected by temperature. Warmer water can hold less oxygen than cooler water. This is because warmer water molecules move faster and are more likely to collide with oxygen molecules, causing them to escape from the water.
Salinity can also affect DO levels. Salt water has a higher salt content than fresh water, and salt can bind to oxygen molecules, making them unavailable for use by aquatic life.
Pollutants can also reduce DO levels. Some pollutants, such as sewage and industrial waste, can contain oxygen-consuming bacteria. These bacteria can quickly deplete the DO in a body of water.
As a result of these factors, DO levels can vary significantly from one body of water to another. It is important to monitor DO levels in order to ensure that they are adequate for aquatic life.
Here is a brief explanation of each option:
- Option A: Maximum at noon. This is the correct answer, as photosynthesis, which produces oxygen, occurs during the day.
- Option B: Minimum at noon. This is incorrect, as DO levels are typically highest during the day.
- Option C: Maximum at midnight. This is incorrect, as DO levels are typically lowest at night.
- Option D: Same throughout the day. This is incorrect, as DO levels can vary significantly from one time of day to another.