National aquatic animal of India is

Crocodile
Tortoise
River Dolphin
Rohu Fish

The correct answer is (c), River Dolphin.

The Ganges River Dolphin is a freshwater dolphin that is found in the Ganges, Brahmaputra, and Meghna river systems in India, Bangladesh, and Nepal. It is the only freshwater dolphin species in India. The Ganges River Dolphin is a shy and elusive animal, and very little is known about its population size or behavior. However, it is believed to be threatened by habitat loss, pollution, and overfishing.

The other options are incorrect for the following reasons:

  • Crocodiles are not aquatic animals. They are reptiles that live in both water and on land.
  • Tortoises are also not aquatic animals. They are reptiles that live on land.
  • Rohu fish is a freshwater fish that is found in India and Bangladesh. It is an important food fish, but it is not the national aquatic animal of India.