Answer: Less than 5 ppm.
- A Less than 5 ppm
- B About 15 ppm
- C Roughly 30-40 ppm
- D More than 100 ppm
Correct answer: A. Less than 5 ppm
Explanation: Clean water has a BOD below 5 ppm; a high BOD indicates heavy organic pollution.
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.