Question

In a polluted lake, the index of pollution is
(a) Presence of frogs
(b) Diatoms larvae
(c) BOD and Daphnia
(d) DO and Artemisia

Answer 1

Hint: These organisms can be found in almost any permanent body of water especially in freshwater and the highest concentrations are found in the vegetation in most lakes and ponds and it reproduces asexually.

Complete answer:
Biological oxygen demand or BOD is the amount of oxygen required by microbes to break down the organic matter present in a particular volume of a water sample. The measure of the amount of organic material in the water is the amount of BOD in the water. BOD is high in polluted water as it contains plenty of organisms. Daphnia, a genus of small planktonic crustaceans, are small organisms (0.2–5 millimeters in length) which are sensitive to pollutants. They are one of the several small aquatic crustaceans and their swimming style resembles the movements of fleas so they are commonly known as water fleas. The more pollutants in the water, the lesser these organisms are in that water. So they are used as bioindicators for water pollution.
Frog they are members of short-bodied amphibians composing the order Anura. They can absorb water through their skin, usually eat meat (bugs and worms) and swallow their food whole. They cannot live in the sea or any water containing salt.
Diatoms (unicellular eukaryotic microalgae) they play important ecological roles on a global scale. They are responsible for 40% of marine primary productivity and 20% of carbon fixation. Also, they are major contributors to climate change processes.
Artemisia is a large genus of plants belonging to the daisy family Asteraceae. People take Artemisia herba-alba for stomach, cough, and intestinal upset. They can also be taken for parasitic infections (like roundworms, pinworms, and tapeworms) , diabetes, jaundice, anxiety, irregular heartbeat, and muscle weakness.
So, the correct answer is option ‘BOD and Daphnia’. 

Note: A substance that has undesired effects, or adversely affects the usefulness of a resource especially water or the atmosphere is known as a pollutant. A few examples of pollutants are ash, smoke, dust, nitric oxide, etc.