Answer : 4. "Sawai Madhopur - Sirohi - Bhilwara - Ajmer "
Explanation :

1. Red and yellow soils are found in the Sirohi, Bhilwara, Sawai Madhopur and Ajmer districts of Rajasthan.

2. The soil has acquired a yellow colour due to a high level of hydration of ferric oxide. The pH of this type of soil ranges between 5.5 to 8.5.

3. Silt loam to silt-clay loam are common in this area.