Choose the incorrect statement:

Correct option is C

The incorrect statement is (c) In dark hours, algae in water bodies increases pH of water. During dark hours (night), algae undergo respiration instead of photosynthesis. This process releases carbon dioxide (CO₂) into the water, which forms carbonic acid, thereby decreasing the pH of the water rather than increasing it.
Explanation:
· Photosynthesis (daytime): Algae consume CO₂ during photosynthesis, reducing carbonic acid levels and increasing the pH of the water.
· Respiration (nighttime): Algae respire in the absence of sunlight, releasing CO₂, which increases the acidity (lowers pH).
· Therefore, the pH tends to decrease during dark hours due to CO₂ accumulation.
Information Booster:
1. Algal blooms can significantly alter water pH levels due to rapid photosynthesis.
2. During the day, algae remove CO₂, causing the pH to rise (alkalinity increases).
3. At night, respiration by algae and other organisms releases CO₂, lowering pH.
4. pH levels in water bodies with algal blooms exhibit diurnal variations (changes over a 24-hour period).
5. High pH (up to 10) can occur in water bodies with extensive blooms due to excess photosynthesis.
6. Extreme pH changes can impact aquatic life and water quality.
Additional Knowledge:
· (a) Water bodies with extensive algal bloom have as high pH as 10:
· Correct. Intense photosynthesis during algal blooms can lead to a pH as high as 10 due to reduced CO₂ levels.
· (b) Removal of CO₂ by photosynthesis by algae is responsible for high pH:
· Correct. Algae consume CO₂ during photosynthesis, reducing acidity and raising pH.
· (c) In dark hours, algae in water bodies increases pH of water:
· Incorrect. At night, algae release CO₂ during respiration, which lowers pH.
· (d) Water bodies with algal bloom experiences diurnal variation in pH:
· Correct. pH fluctuates due to photosynthesis (day) and respiration (night).
Key Points:
1. Photosynthesis increases pH by removing CO₂.
2. Respiration decreases pH by releasing CO₂.
3. Algal blooms cause diurnal pH variations.
4. High pH can harm aquatic organisms.
5. Monitoring pH is essential for maintaining water quality.