Which is the largest botanical garden in the world? Name a few well known Botanical gardens in India.

The largest botanical garden in the world is Royal Botanical Garden (RBG, Kew, London)
The famous well known botanical gardensin India are
(i) Indian Botanical Garden, Sibpur, Kolkata.
 
(ii) Lloyd Botanical Garden, Darjeeling.
 
(iii) Botanical Garden of FRI, Dehradun (UK).
 
(iv) National Botanical Garden (NBG) Lucknow, UP