Answer : 4. "Gujarat "
Explanation :

1. The longest coastline in India is along the state of Gujarat. Its length is approximately 1,600 kilometres. This coastline borders the Arabian Sea and includes many beautiful beaches, islands and ports.

2. Gujarat's coastline is important for India's economy and culture. It is an important centre for tourism, fishing and trade. Several important ports are also located on the coastline, such as Mundra, Kandla and Porbandar.