Assertion : There is a sharp decline in dissolved oxygen downstream from the point of sewage discharge.
Reason : Microoganisms ionvolved in biodegradation or organic matter in the receiving water body consume a lot of oxygen.

Assertion: Discharge of sewage into river results into a sharp details in disolved oxygen Reason:- Micro-organisms invovled in biodegradation of organic matter in the reciving water body produce a lot of oxygen to facilitate degration of organic matter.

Assertion (A) : The lower the concentration of DO , the the more polluted is the water sample. Reason (R) : Oxygen is consumed by microbes for the decomposition of organic matter present in water.

Assertion: Elchhornia crassipes increases the oxygen content of water bodies. Reason: Anoxic condition in water boidies leads to Eutrophication.

Assertion: Sewage discharge in a water body causes eutrophication. Reason: This increases the organic content in water body and, hence, the growth of algal blooms.

Assertion: Sewage discharge in a water body causes eutrophication. Reason: This increases the organic content in water body and, hence, the growth of algal blooms.