Answer : 3. "South-Eastern Region"
Explanation :

1. Out of the following, alluvial soil is mainly found in the group of Kota-Bundi districts of Rajasthan.

2. Deficiency of calcium and phosphate elements and excess of nitrogen and potash are found in this soil.

3. For this reason, alluvial soil is considered to be the most fertile soil in Rajasthan.

4. Mainly mustard, wheat, rice, cotton, sugarcane etc. are produced in this soil.