Question

Given below are two statements : Statement I : The value of the parameter “Biochemical Oxygen Demand (BOD)” is important for survival of aquatic life. Statement II : The optimum value of BOD is 6.5 ppm. In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Low BOD = Clean Water; High BOD = Polluted Water. Don't confuse BOD with DO (Dissolved Oxygen). For DO, higher is generally better for fish; for BOD, lower is better.

Answer 1

The Correct Option is C

Step 1: BOD is a measure of the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material. High BOD means lower dissolved oxygen for fish, so it is crucial for aquatic survival.
Step 2: "Clean" water has a BOD value of less than 5 ppm. Highly polluted water has BOD of 17 ppm or more. 6.5 ppm is actually a slightly polluted value, not an "optimum" standard (which should be as low as possible).
Step 3: Note that Statement II often confuses BOD with Dissolved Oxygen (DO), where an optimum value for aquatic life is indeed around 4–6 ppm.