Answer: oxygen.
- A oxygen
- B carbon dioxide
- C nitrogen
- D hydrogen
Correct answer: A. oxygen
Explanation: BOD measures the oxygen microbes use to decompose organic matter in water.
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.