Answer : 4. "खेजड़ी"
Explanation :

1. The state tree of Rajasthan is Khejri. This tree is found in about two-thirds of the total geographical area of the state and has great importance culturally and economically.

2. The scientific name of Khejri is Prosopis cinerea. It is a drought-tolerant tree that can survive even in areas with low rainfall. This tree is found in desert areas and is found in abundance in the Thar Desert of Rajasthan.