The quantity of oxygen that is essential for microorganisms to break down the biological substance existing in a specific capacity of a sample water is called ______________.Select one:a.Marine Necessityb.Thermal demand of oxygenc.Chemical oxygen demandd.Biochemical oxygen demand

The correct answer is d. Biochemical oxygen demand.

Here's the step-by-step reasoning:

1. Understanding the Question: The question asks for the term that describes the quantity of oxygen required by microorganisms to break down biological substances in a water sample.

2. Analyzing the Options:

   • a. Marine Necessity: This term does not relate to the oxygen required by microorganisms for breaking down substances.
   • b. Thermal demand of oxygen: This term is not commonly used in the context of water quality and oxygen requirements for microorganisms.
   • c. Chemical oxygen demand: This measures the total quantity of oxygen required to oxidize both organic and inorganic substances in water, but it does not specifically refer to the oxygen needed by microorganisms.
   • d. Biochemical oxygen demand: This specifically measures the amount of oxygen that microorganisms need to break down organic material in water.

3. Conclusion: The term that fits the description given in the question is Biochemical oxygen demand.

Therefore, the correct answer is d. Biochemical oxygen demand.