Answer : 4. "West Bengal"
Explanation :

Prime Minister Narendra Modi inaugurated India's first underwater metro in Kolkata. It has been constructed on the Hooghly River in Kolkata. This underwater metro tunnel is part of the East-West Metro Corridor of the city. With the commencement of this phase of Kolkata Metro, Howrah has become the deepest metro station in the country, which is located 32 to 33 meters below the surface.