Answer: Nitrates and phosphates from agricultural runoff and sewage.
- A Heavy metals such as lead and mercury in most textbook accounts
- B Nitrates and phosphates from agricultural runoff and sewage
- C Carbon dioxide from fossil fuel combustion during normal conditions
- D Sediment and clay particles from construction sites as generally observed
Correct answer: B. Nitrates and phosphates from agricultural runoff and sewage
Explanation: Eutrophication is driven by excessive nitrogen and phosphorus from fertilisers and sewage. These nutrients trigger algal blooms, which deplete dissolved oxygen when the algae die and decompose, causing hypoxia and death of aquatic organisms.
Classical smog is a reducing mixture of SO₂ and fog, while photochemical smog is an oxidising mixture generated by UV-driven reactions of NOx and hydrocarbons.
Concept context
Understand how human activities alter the atmosphere, water, and soil. Covers air pollutants, smog types, ozone depletion, acid rain, greenhouse effect, water and soil pollution, and the principles of green chemistry.