Answer: Clean water has high dissolved oxygen and low BOD.
- A Clean water has low dissolved oxygen and high BOD
- B Clean water has high dissolved oxygen and low BOD
- C Both dissolved oxygen and BOD are high
- D Both dissolved oxygen and BOD are low to zero
Correct answer: B. Clean water has high dissolved oxygen and low BOD
Explanation: Clean water holds ample dissolved oxygen and has a low BOD; a high BOD signals heavy organic pollution that depletes the dissolved oxygen.
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.