Water for Life

1. What is the pH value of pure, neutral water?

• A) 5
• B) 6
• C) 7
• D) 8

2. At which temperature does water reach its maximum density?

• A) 0° Celsius
• B) 4° Celsius
• C) 100° Celsius
• D) -1° Celsius

3. According to the text, what are the largest sources of water on Earth?

• A) Rivers and lakes
• B) Glaciers and snow
• C) Seas or oceans
• D) Groundwater

4. What is the chemical formula for a water molecule?

• A) HO₂
• B) H₂O
• C) O₂H
• D) H₂O₂

5. How does turbid water primarily harm aquatic plants?

• A) It increases the water's salinity.
• B) It lowers the water's pH to acidic levels.
• C) It introduces infectious microorganisms.
• D) It hinders sunlight penetration, reducing photosynthesis.

6. Why does the Hilsha fish migrate from saline sea water to fresh river water for spawning?

• A) To find a warmer environment for its eggs.
• B) Because fresh water has more dissolved oxygen.
• C) To avoid sea predators during the vulnerable spawning period.
• D) Because the high salt content in sea water sterilizes the fish eggs.

7. What is the minimum level of dissolved oxygen required to sustain life in water bodies?

• A) 1 mg/litre
• B) 3 mg/litre
• C) 5 mg/litre
• D) 10 mg/litre