Under Ganga Action and Yamuna Action plans, it is proposed to -

The correct answer is Option (3) → Discharge only the treated sewage into both the rivers

Option (1) Directly discharge the water from industry into the rivers — Incorrect. Untreated industrial waste water pollutes the rivers. The plans were started to save the rivers from pollution, so they cannot propose this.

Option (2) Discharge untreated sewage into the Yamuna river — Incorrect. Untreated sewage is the very problem the plans try to solve. It is already let into rivers because there are too few treatment plants, and it spreads water-borne diseases.

Option (3) Discharge only the treated sewage into both the rivers — Correct. The Ganga Action Plan and the Yamuna Action Plan propose to build a large number of sewage treatment plants. In these plants microbes remove most of the organic matter, so only treated sewage reaches the two rivers.

Option (4) Discharge water with high BOD into the rivers — Incorrect. A high BOD means the water holds a lot of organic matter. Microbes use up the oxygen of the river to break it down, and fish die. Sewage is treated until its BOD is low.

NCERT Extract:
Microbes in Sewage Treatment – …