Oxygen in Natural Water Sources

Steps:

• Identify key processes in natural water: Photosynthesis by algae and plants releases oxygen for aquatic life.
• Review domestic water treatment: Chlorination disinfects; sedimentation settles solids; tastes/odors use filtration or carbon.
• Assess pollution impacts: Detergents cause eutrophication via phosphates, not metals, leading to oxygen depletion.
• Check nitrate removal: Requires biological or chemical methods, not sedimentation.

Why C is correct:

• Photosynthesis equation (6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂) shows aquatic plants produce dissolved oxygen essential for fish and organisms.

Why the others are wrong:

• A: Chlorine disinfects pathogens; tastes/odors are removed by activated carbon or aeration.
• B: Detergents' phosphates cause algal blooms and deoxygenation; metal compounds are not primary from detergents.
• D: Sedimentation removes suspended particles; nitrates are dissolved and need ion exchange or denitrification.

Final answer: C