Decreasing dissolved oxygen (DO) level in a water body A. Severely threatens…
2023
Decreasing dissolved oxygen (DO) level in a water body
A. Severely threatens aquatic life
B. is mainly caused by oxygen-demanding wastes
C. indicates the presence of biodegradable organic substances
D. causes undesirable taste and colour
E. makes it non-drinkable for human beings
Choose the correct answer from the options given below:
Answer: A. A, B, C, D only — CONCEPTDissolved oxygen (DO) is the oxygen available in water for aquatic respiration. Organic pollution raises biochemical oxygen demand (BOD):…
- A.
A, B, C, D only
- B.
B, C, D, E only
- C.
A, C, D, E only
- D.
A, B, D, E only
Show answer & explanation
Correct answer: A
CONCEPT
Dissolved oxygen (DO) is the oxygen available in water for aquatic respiration.
Organic pollution raises biochemical oxygen demand (BOD): microorganisms consume oxygen while decomposing biodegradable matter, so DO falls when oxygen demand exceeds reaeration and photosynthetic supply.
APPLICATION
A. Aquatic organisms require DO; severe depletion causes hypoxic stress and can cause mortality.
B. Oxygen-demanding wastes promote microbial oxidation, which consumes DO.
C. Low DO can therefore indicate biodegradable organic loading and elevated BOD.
D. Oxygen depletion encourages anaerobic conditions and reduced compounds that can produce objectionable taste, odour, and colour.
E. DO is an important water-quality indicator, but low DO alone is not a universal drinking-water potability criterion; drinking suitability requires separate microbiological, chemical, and sensory tests.
CROSS-CHECK / CONTRAST
A set that omits A loses the direct effect of hypoxia on aquatic respiration.
A set that omits B loses the oxygen-consumption mechanism created by oxygen-demanding waste.
A set that omits C loses the BOD–DO indicator relationship.
The set A, B, C, D only retains those established relationships while excluding the overbroad potability claim E.
RESULT
The correct combination is A, B, C, D only.