The state in India with the longest coastline is Gujarat.

Gujarat, located in the western part of India, has the longest coastline among all the states in the country. It is surrounded by the Arabian Sea to the west, making it a coastal state with a vast shoreline.

Reasons why Gujarat has the longest coastline:
- Geographic Location: Gujarat is situated in the western region of India, bordering the Arabian Sea. Its strategic location makes it naturally blessed with a long coastline.

- Arabian Sea: Gujarat shares its western border with the Arabian Sea, which provides the state with a vast coastal area. The Arabian Sea is a body of water that separates the Indian subcontinent from the Arabian Peninsula, and Gujarat benefits from its proximity.

Key facts about Gujarat's coastline:
- Length: Gujarat has a coastline that stretches approximately 1,600 kilometers (994 miles) along the Arabian Sea. This makes it the state with the longest coastline in India.

- Beaches: The coastline of Gujarat is adorned with numerous beautiful beaches, attracting tourists from all over the world. Some of the famous beaches include Mandvi Beach, Dwarka Beach, and Diu Beach.

- Ports: Gujarat's long coastline has also contributed to the development of several major ports. The state has some of the busiest ports in India, such as the Kandla Port, Mundra Port, and Pipavav Port. These ports play a significant role in international trade and facilitate the movement of goods and commodities.

- Marine Life: The coastline of Gujarat is home to a rich variety of marine life. It provides habitats for various species of fish, turtles, and dolphins. The state also has marine national parks, such as Marine National Park in the Gulf of Kutch, which protect and conserve the marine ecosystem.

In conclusion, Gujarat has the longest coastline among all the states in India due to its strategic location along the Arabian Sea. The state's coastline stretches approximately 1,600 kilometers and is known for its beautiful beaches, busy ports, and diverse marine life.