The correct answer is (a) Yamuna.
The Yamuna is one of the most polluted rivers in India. It is called a “biological desert” because it is so polluted that very few plants or animals can live in it. The main pollutants in the Yamuna are sewage, industrial waste, and agricultural runoff. These pollutants have caused the river to become very dirty and toxic.
The Yamuna is a sacred river for Hindus, and it is a major source of drinking water for millions of people. However, the pollution in the Yamuna has made it unsafe to drink or bathe in. The pollution has also caused the river to become a breeding ground for diseases, such as cholera and typhoid.
The Indian government has taken some steps to clean up the Yamuna, but the problem is very complex and difficult to solve. The government needs to do more to reduce the amount of pollution that is being dumped into the river. It also needs to educate people about the importance of keeping the river clean.
The other options are incorrect because they are not as polluted as the Yamuna. The Periyar is a river in India that is known for its beauty and its biodiversity. The Damodar is a river in India that is heavily polluted, but it is not as polluted as the Yamuna. The Mahanadi is a river in India that is moderately polluted.