Question

___ indicate(s) that a waterbody is polluted.

• A. Presence of lichens
• B. Absence of lichens
• C. Absence of snails
• D. Algal boom

Answer 1

Answer: (C), (D)

The correct options are
C Absence of snails
D Algal boom

Snails are bio indicators that can not exist in polluted water. Absence of snails near a water body indicates that the water is polluted.

Algal bloom is a result of excessive accumulation of nutrient rich pollutants into water bodies. It results in eutrophication which increases oxygen demand for decomposing the organic matter. Hence, the amount of oxygen in the waterbody decreases.

Lichens are indicators of air pollution.