Question

BOD stands for
A. Biological oxygen demand
B. Chemical oxygen demand
C. Biodegradation
D. Biotic community

Answer 1

Hint: As we are already aware that aerobic microorganisms need oxygen to decompose the organic substances present in water or waste water at a specific temperature and for a specific period of time. If the value of this term is low in water then we assume that the water quality is good and thus it is safe for drinking.

Complete answer:
As we know that the amount of dissolved oxygen (DO) used up by the aerobic microorganisms to decompose the organic matter present in a sample of water is termed Biological Oxygen Demand or Biochemical Oxygen Demand (BOD).
So, BOD is an indirect measure of the concentration of readily biodegradable organic matters. BOD concentration of wastewater is expressed in $mg{L^{ - 1}}$ and the BOD of clean water is $2mg{L^{ - 1}}$. When the value of BOD exceeds $5mg{L^{ - 1}}$it indicates contamination of water.
We should remember that since aerobic microorganisms live by decomposing organic matters, the amount of oxygen used is proportional to their number and metabolic rate.
Let us now discuss the chemical oxygen demand which is basically used as a measure of oxygen requirement of a sample that is susceptible to oxidation by a strong chemical oxidant.
Under controlled conditions of temperature and time, a chemical oxidising agent like potassium permanganate or potassium dichromate is added to the sample of water and the amount needed to oxidise the reducing material is measured.
Next comes biodegradation which is basically the process of degradation of organic substances by the microorganisms chiefly the aerobic bacteria.
And lastly we have a biotic community which is a group of organisms that live together in a community and interact with each other for food and other sources. For instance: plants and animals.
Therefore, from the above explanation we can say that BOD stands for Biological Oxygen Demand.

Hence, the correct answer is (A).

Note:
Remember that the BOD test evaluates the dissolved oxygen used up by aerobic microorganisms over a five days period at a temperature of 20 degree celsius.. When BOD levels are high, there is a decline in the DO levels meaning that the microorganisms are using most of the dissolved oxygen.