Biological Oxygen Demand (BOD) is a standard criterion for
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Answer: C. Biological Oxygen Demand is the amount of dissolved oxygen that microbes need to break down organic matter in a water sample. A high BOD means a lot of organic pollution. It is a standard test of water pollution. So option C.
Watch for: The word 'biological' can pull you toward blood or forests; BOD is about water.
Why the other options are wrong
- A. Wrong because blood oxygen is measured as oxygen saturation, not BOD.
- B. Wrong because BOD is a water test, not a forest test.
- D. Wrong because BOD has nothing to do with air oxygen at altitude.
Source to check: NCERT Class 12 Biology, Chapter 10 'Microbes in Human Welfare' (sewage treatment) and Class 12 Biology (old edition), Chapter 16 'Environmental Issues'; CPCB water quality criteria (cpcb.nic.in)
Answer from the official UPSC key. Written and fact-checked by AI against the official key. Spotted a mistake? Report it.