Answer: nitrate and phosphate runoff.
- A clean oxygen-rich water
- B harmless river sediment
- C nitrate and phosphate runoff
- D cool underground water
Correct answer: C. nitrate and phosphate runoff
Explanation: Runoff carrying nitrates and phosphates from fertilisers and sewage enriches the lake with nutrients, causing algal blooms and oxygen depletion (accelerated eutrophication).
Sunlight passes through the atmosphere and warms the surface; the surface re-radiates this energy as infrared heat, which greenhouse gases (CO₂, CH₄, water vapour) absorb and trap - a naturally beneficial process that intensifies into global warming as gas concentrations rise from human activity.
Concept context
Pollution, global warming, ozone depletion, deforestation, and sustainability. Important for NEET and general awareness.