Answer : 2. "शुष्क पश्चिमी मैदानी खण्ड "
Explanation :

1. Rajasthan's agriculture is divided into 10 parts on the basis of crop climate zone.

2. In terms of area, the largest agro-climatic zone of Rajasthan is I-C (extremely dry partially irrigated zone).

3. Rajasthan's smallest agricultural crop in terms of area is climate zone IV-B.

4. On the basis of agricultural area, the largest agricultural crop in Rajasthan is climate zone III-B.