The southernmost tip of the mainland of India is Kanyakumari.

The southernmost tip of the mainland of India is located in the state of Tamil Nadu and is known as Kanyakumari. Let's understand why Kanyakumari is considered the southernmost tip with the help of some key points:

Geographical Location:
- Kanyakumari is situated at the meeting point of the Arabian Sea, the Bay of Bengal, and the Indian Ocean.
- It is located at the southernmost point of the Indian peninsula, where the mainland of India tapers into the Indian Ocean.

Latitude and Longitude:
- Kanyakumari is located at a latitude of 8.0883° N and a longitude of 77.5385° E.
- These coordinates mark the southernmost point of the mainland of India.

Distance from Other Cities:
- Kanyakumari is approximately 90 kilometers away from Thiruvananthapuram, the capital city of the neighboring state of Kerala.
- It is around 700 kilometers away from Chennai, the capital city of Tamil Nadu.
- Mumbai, which is located in the western part of India, is much farther away from Kanyakumari.

Important Landmarks:
- At Kanyakumari, there is a famous landmark called the Vivekananda Rock Memorial. It is a rock island located around 400 meters off the coast of Kanyakumari.
- The Thiruvalluvar Statue, a 133-feet tall stone statue of the famous Tamil poet and philosopher Thiruvalluvar, is also situated near Kanyakumari.

Cultural Significance:
- Kanyakumari is known for its religious and cultural significance. It is a popular pilgrimage site for Hindus, as there is a temple dedicated to the goddess Kanyakumari (also known as Devi Kanya Kumari) at this location.
- The place is also famous for its beautiful sunrise and sunset views, where one can witness the convergence of the three bodies of water.

In conclusion, Kanyakumari is considered the southernmost tip of the mainland of India due to its geographical location, latitude and longitude coordinates, and its cultural and historical significance.