The Botanical Survey of India is headquartered in Kolkata, which is option 3. This means that the main office of the organization is located in Kolkata. Option 1, Lucknow, is incorrect as it is not the correct location for the Botanical Survey of India. Option 2, Darjeeling, is also incorrect as the organization`s headquarters are not in Darjeeling. Option 4, Oottaccamund, is also incorrect as it is not the correct location for the Botanical Survey of India. It is important to note that the Botanical Survey of India is responsible for surveying and documenting the plant resources of the country, and its headquarters being in Kolkata signifies the importance of the city in botanical research and conservation efforts in India.