If you want to see gharials in their natural habitat, the best place to visit is the Chambal River, Option 2.

The Chambal River is a major tributary of the Yamuna River, and it flows through India`s states of Madhya Pradesh, Rajasthan, and Uttar Pradesh. It is home to one of the world`s largest populations of gharials. These critically endangered crocodilians are known for their long, narrow snouts, which they use to catch fish. The Chambal River is also home to other crocodilians such as mugger crocodiles and saltwater crocodiles.

The Chambal River is a relatively undisturbed river, with very little human activity along its banks. This makes it an ideal habitat for gharials, which are sensitive to disturbances such as pollution and human encroachment. The river also has a healthy fish population, which is the primary food source for gharials.

In contrast, the other options mentioned in the question do not have as large or healthy populations of gharials.

Bhitarkanika Mangroves, Option 1, is located in the Indian state of Odisha and is home to saltwater crocodiles, but the population of gharials is relatively small.

Pulicat Lake, Option 3, is a brackish water lagoon located on the border of Andhra Pradesh and Tamil Nadu. While it is home to several species of fish, the population of gharials is not significant.

Deepor Beel, Option 4, is a freshwater lake located in Assam and is home to a variety of aquatic species, including some crocodiles, but the population of gharials is not as significant as that of Chambal River.

In summary, if you want to see gharials in their natural habitat, the Chambal River, Option 2, is the best place to visit. It offers a pristine environment, with a healthy population of gharials, and is relatively undisturbed by human activity.