Which statement best describes BOD in the notes?

• A. Hard, complex, larger compounds may take hrs or days, attacked by enzymes secreted by bacteria
• B. Better measure of toxicity, soft, simple, more easily degraded, 1-2 hrs
• C. Both A and B
• D. None of the above

Answer: (B)

Biochemical oxygen demand shows how much oxygen microbes need to oxidize organic matter in water. The notes describe BOD as a measure of how readily organics can be biodegraded by bacteria, with simpler, softer molecules being attacked more easily and degraded faster, often represented by a shorter timescale like 1–2 hours. Because of that, the statement that BOD is a better measure of how easily organics are degraded and that simple compounds degrade quickly lines up best with the notes. The idea that BOD measures toxicity isn’t accurate to what BOD assesses, and the notion about hard, complex compounds taking longer reflects biodegradation in general but doesn’t match the notes’ emphasis on readily biodegradable substances and quicker degradation. So the best fit is describing BOD as a measure tied to biodegradability and rapid degradation of simple organics.