Answer: Heavily polluted water with a high organic load.
- A Highly pure drinking water overall in most cases
- B Low dissolved mineral content under typical conditions
- C Presence of dissolved toxic metals mainly
- D Heavily polluted water with a high organic load
Correct answer: D. Heavily polluted water with a high organic load
Explanation: BOD measures oxygen consumed by microbes decomposing organic matter in water over 5 days at 20 degrees C. A high BOD means large amounts of organic waste are present. Clean water has BOD below 5 ppm; very polluted water exceeds 17 ppm.
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.