The correct answer is option 3, Orissa. The largest brackish water lake in India is Chilika Lake, which is located in the state of Orissa. Brackish water is a mix of freshwater and saltwater, with a salinity level higher than freshwater but lower than seawater. Chilika Lake covers an area of about 1,100 square kilometers and is considered as one of the largest coastal lagoons in the world. It is home to a diverse range of flora and fauna, including various species of birds, fish, and dolphins. The lake is also an important habitat for migratory birds and has been recognized as a Ramsar site, which is a wetland of international importance.